Summarize the following court judgment. Civil Appeals Nos. 2221 2225	 and 2524 of 1972. From the Judgment and orders dated the 18 11 71	 29 3 1972 and 5 2 1972 of the Delhi High Court in L.P. No. 53/71 and Civil Writ Petitions Nos. 612	 640	 643 and 649/71	 281/72 and 1052 of 1971 respectively. A.K. Sen	 Sarjoo Prasad Balram Senghal and C. P. Lal for the Appellants in CAs 2221 2225/72 B. Sen	 S.P. Nayar and M.N. Shroff for Respondents 2 3	 (In CAs. 2221 2225/72) for Respondents 1 4 in.C.A. 1801). S.V. Gupte	 Mrs. Leila Sait and U. K. Kaithan for Interveners (In CAs.2221 2225/72) and Appellants (In CAs.2524/72). M. C. Bhandare	 Sardar Bahadur Saharya	 B. N. Kirpal and V. B. Saharya for the Appellant in CA 1801/72. The Judgment of the Court was delivered by SARKARIA	 J. Whether the Notification No. SRO 2908	 dated December 7	 1957 issued by the Central Government in purported exercise of its powers under section 2 of the Union Territories (Laws) 	 is ultra vires the Central Government is the principal question that arises in these appeals which will be disposed of by a common judgment. The question has arisen in these circumstances: Section 2 of the Part States (Laws) Act	 1950	 empowered the Central Government to extend by notification in the official Gazette to any Part State	 or to any part of such State	 with such restrictions and modifications as it thinks fit	 any enactment which is in force in a Part A State. In exercise of this power	 the Central Government by a Notification No. SRO 615 dated the 28th April 1951	 extended to the then Part State of Delhi	 the Bengal Finance (Sales Tax) Act	 1941 (for short	 the Bengal Act)	 with	 inter alia	 these modifications: "In sub section (2) of Section 6	 (a)(b) for the words "add to the Schedule"	 the words "add to or omit or otherwise amend the Schedule" shall be substituted " For the Schedule of the Bengal Act	 this Notification substituted a modified Schedule of goods exempted under section 6. The relevant items in the modified Schedule were as follows: "8.Fruits	 fresh and dried (except when sold in sealed containers) Pepper	 tamarind and chillies.Turmeric. Cloth of such description as may from time to time be specified by notification in the Gazette costing less per yard than Rs. 3/ or such other sum as may be specified. 21A. Knitting wool. " Section 6 of the Bengal Act after its extension to Delhi	 as modified by the said Notification	 reads thus : "6(1)No tax shall be payable under this Act on the sale of goods specified in the first column of the Schedule subject to the conditions and exceptions if any set out in the corresponding entry in the second column thereof. (2) The State Government after giving by Notification in the official Gazette not less than 3 months ' notice of its intention so to do may by like notification 790 add to or omit from or otherwise amend the Schedule and thereupon the Schedule shall be deemed to be amended accordingly." (emphasis supplied) By a Notification	 dated 1 1 1951	 in sub section (1) of section 6	 the words "the first column of" were omitted and for the words "in the corresponding entry in the second column thereof" the word "therein" was substituted. By a notification country liquor was included in the Schedule as item No. 40 of exempted goods with effect from 19 1 1952. On 1 11 1956	 as a result of the coming into force of the States Reorganization Act	 1956	 and the Constitution (Seventh Amendment) Act	 1956	 Part States were abolished. Part State of Delhi became a Union Territory and the Delhi Legislative Assembly	 was also abolished. In 1956	 Part State (Laws) Act	 1950 (hereinafter referred to as Laws Act) also became me 	 with necessary adaptations. On 1 12 1956	 Parliament passed the Bengal Finance (Sales Tax) (Delhi Amendment) Act 1956 which introduced amendments in different sections of the Bengal Act as applicable to Delhi. It made only two changes in section 6 Firstly	 the word 'Schedule '	 wherever it occurred	 was replaced by the words "Second Schedule". Secondly the words "Central Government" were substituted for the words "State Government". On December 7	 1951	 in the Gazette of India Extraordinary there appeared a notifications which reads as below: "S.R.O. 3908 In exercise of the powers conferred by section 2 of the (30 of 1950)	 the Central Government hereby makes the following amendment in the notification of the Government of India in the Ministry of Home Affairs No. S.R.O. 615	 dated the 28th April	 1951 (extending to the Union Territory of Delhi and the Bengal Finance (Sales Tax) Act	 1941	 subject to certain modifications) namely : In the said notification	 in the modifications to the Bengal Act aforesaid	 in item 6 (relating to sub section (2) of section (6)	 after sub item (a)	 the following sub item shall be inserted	 namely : "(aa) for the words "not less than three months ' notice	 the words such previous notice as it considers reasonable" shall be substituted". The vires of this notification dated 7 12 1957	 is me subject of primary challenge in these appeals (hereinafter it will be referred to as the impugned notification). 791 Item 17 in the Second Schedule of the Bengal Act was amended with effect from December 14	 1957 by Notification No. SRO 3958	 as under : "17. All varieties of cotton	 woollen	 rayon or artificial silk fabric but not including real silk fabrics". "Conditions subject to which tax shall not be payable: In respect of tobacco cotton fabrics	 rayon or artificial silk fabrics and woollen fabrics as defined in item 9	 12	 12A	 12B at the First Schedule to the (I of 1944) included in entries (a) and (c) above	 no tax under the Bengal Finance (Sales Tax) Act 1941	 shall be payable in the Union Territory of Delhi only if additional duties of excise have been levied on them under the Additional Duties of Excise (Goods of Special Importance) Act 1957". The aforesaid condition was withdrawn by Notification No. GSR 203	 dated 1 4 1958. By Notification No. GSR 202	 dated 1 4 1958	 the Central Government withdrew the exemption of country liquor from tax by omitting item No. 40 from the Second Schedule. By Notification No. GSR 1076 dated 19 9 1959	 the Central Government withdrew the exemption from tax of Items	 8	 11	 14 and 21A by omitting them from the Second Schedule with effect from 1 10 1959. On 1 10 1959	 the Bengal (Sales Tax Delhi Amendment) Act	 1959 (Act XX of 1959) came into force whereby Parliament made some amendments in different sections of the Bengal Act but left section 6 untouched. By a Notification No. GSR 964 dated 16 6 1966	 notice was given that item 17 of the Second Schedule would be substituted with effect from 1 7 1966	 as follows: "Item 17 All varieties	 cotton	 woollen	 nylon	 rayon	 pure silk or artificial silk fabrics but excluding Durries	 Druggets and carpets". The proposed amendment was given effect to from 1 7 1966	 by Notification No. GSR 1061 dated 29 6 66. One result of this amendment was that exemption of Durries from tax was withdrawn	 while	 such exemption was among others	 extended to 'pure silk '. By a Notification GSR 1038	 dated 14 7 1970	 notice was given that item 17 in the Second Schedule would be substituted with effect from 1 8 1970	 as follows: "17.All varieties of cotton fabrics	 rayon	 or artificial silk fabrics and woollen fabrics but not including Durries	 Druggets and carpets". 792 Such substitution of item 17 was made with effect from 1 8 70 by Notification GSR 1119 dated 31 7 1970. one result of this notification was that the exemption of 'pure silk ' from tax was withdrawn. The appellants in Civil Appeal No. 2221 of 1972 are dealers in durries. They feel aggrieved by the Notification GSR 1061 dated 29 6 1966 whereby exemption of Durries from sales tax was withdrawn. The appellants in Civil Appeals 2222	 2223 and 2225 of 1972 deal in knitting wool. Their cause of action arose when exemption of knitting wool was withdrawn by Notification dated 19 9 1959	 w.e.f. 1 10 1959. The appellants in Civil Appeals 2524 of 1972 deal inter alia in pure silk. They are aggrieved by Notification	 dated 31 7 1970 by which exemption of 'pure silk ' was withdrawn w.e.f. 1 8 1970. The appellants in Civil Appeal No. 2224 of 1972 is a Kiryana dealer. He feels aggrieved by the Notification dated 19 9 1959 whereby items 8	 11 and 14 were deleted from the Second Schedule with effect from 1 10 1959. The appellants in Civil Appeal No. 1801 of 1972 are licensed vendors of country liquor. They feel adversely affected by Notification GSR 1076	 dated 19 9 1959 whereby exemption of country liquor from tax was withdrawn with effect from 1 10 1959. Several writ petitions were filed in the High Court to question the validity of the Government action withdrawing the exemptions with notice far less than three months. A learned Judge of the High Court allowed eight of these petitions by a common judgment recorded in Civil Writ 574 D of 1966	 Lachmi Narain vs Union of India and others. Against that judgment	 the Revenue carried appeals under Clause 10 of the. 	 to a Bench of the High Court. In the meanwhile more writ petitions (C. Ws.593 to 652	 792 to 806 of 1971) were instituted in which the same question was involved. The Division Bench	 by a common judgment	 allowed the appeals and dismissed the writ petitions. The writ petitioners have now come in appeal to this Court on the basis of a certificate granted by the High Court under Article 133 (1) (a) and (c) of the Constitution. In the High Court the validity of the withdrawal of the exemptions was challenged on these grounds : (I) The power given by section 2 of the Laws Act to the Central Government to extend enactments in force in a State to a Union Territory with such restrictions and modifications as it thinks fit	 could be exercised only to make such modifications in the enactment as were necessary in view of the peculiar local conditions. The modification in section 6(2) of the BengaI Act made by SRO 3908	 dated 793 7 10 1957	 was not necessitated by this reason. It was therefore	 ultra vires section 2 of the Laws Act; (2) Such a modification could be made only once when the Bengal Act was extended to Delhi in 1951. No modification could be made after such extension. (3) The modification could not change the policy of the legislature reflected in the Bengal Act. The impugned modification was contrary to it	 and (4) The modifications giving notice to withdraw the exemptions and the notifications issued pursuant thereto withdrawing the exemptions from sales tax with respect to Durries	 Ghee	 (and other items relevant to these petitions) were void as the statutory notice of not less than three months as required by section 6(2) prior to its modification by the impugned notification of 7th December	 1957 had not been given. Finding on all the four grounds in favour of the writ petitioners	 lie learned Single Judge declared "that the purported modification of section 6(2) of the Bengal Finance (Sales Tax) Act 1941 by the Government of India 's notification No. SRO 3908	 dated 7th December	 1957	 was ineffective and section 6(2) continues to be the same as before as if it was not so modified at all." In consequence he quashed the Government notifications GSR 964	 dated 16 6 1966 and GSR 1061 dated 29 6 1966 because they were not in compliance with the requirement of section 6(2) of the Bengal Act. The contentions canvassed before the learned Single Judge were repeated before the appellate Bench of the High Court. The Bench did not pointedly examine the scope of the power of modification given to the Central Government by section 2 of the Laws Act with specific reference to the purpose for which it was conferred and its precise limitations. It did not squarely dispel the reasoning of the learned Single Judge that the power of modification is an integral part of the power of extension and "cannot therefore be exercised except for the purpose of the extension". It refused to accept that reasoning with the summary remark "from the extracts quoted by the learned Single Judge from the judgment of the Supreme Court in Re: Delhi Laws Act and from the Judgment in Rajnarain Singh vs The Chairman Patna Administration Committee Patna and Anr	 the principle deduced by the learned Judge does not appear to follow. We are therefore not inclined	 as at present advised to support the above observations". The Bench however hastened to add : "However	 since the matter was not argued at great length and the appellants ' Counsel rested his submissions on the other aspects of the case	 we would not like to express 794 any definite opinion on the question as to whether the power of making any modifications or restrictions in the Act can only be exercised at the time of extending the Act and that it cannot be done subsequently by the Central Government in exercise of its power." " Seeking support from the observations of this Court in Raza Buland Sugar Co. Ltd. vs Municipal Board	 Rampur	(1) the Bench held that what is mandatory in section 6(2) is the requirement as to the giving of reasonable notice of the Government 's intention t(! amend the second Schedule	 for the information of the public	 and that "no special significance or sanctity is attached to the span of time of three months provided in subsection (2) of section 6." The Bench found that since the withdrawals of the exemptions in question	 had been made after reasonable notice	 the same were not invalid. However	 the main ground on which the decision of the Bench rests is that the infirmity	 if any	 in the impugned notification dated 7 12 1957	 had been cured and rectified when "Parliament while enacting the Amendment Act	 1959 (Act No. '70 of 1959) put its seal of approval to the curtailed period of notice. As such the curtailed period of notice shall be taken to have been provided by Parliament on the ratio of Supreme Court 's decision in Venkatrao Esajirao limberkar 's case". Apart from the grounds taken in their writ petitions	 the learned Counsel for the appellants have tried to raise before us another ground under the garb of what they styled. as merely an additional argument". They now seek to challenge the vires of the Notification SRO 615	 dated the 28th April	 1951 in so far as it relates to the insertion in sub section (2) of section 6 of that Act	 between the words "add to" and "the Schedule"	 of the words "or omit or otherwise amend". It is argued that this insertion was beyond the power of modification conferred on the Central Government by section 2 of the Laws Act. The point sought to be made out is that if the insertion made by the Notification dated 28 4 1951	 in sec.6(2) was ineffective and non est in the eye of law	 the Central Government would have no power to "omit" anything from the exempted goods itemised in the Schedule. It is argued that under section 6(2) sans this insertion	 the Central Government was empowered only to "add to" and not "omit" from the exempted items enumerated in the Schedule	 and consequently	 the withdrawal of the exemptions in question was ultra vires the Central Government. The entertainment of this Plea at this stage is stoutly opposed by Shri B. Sen	 learned Counsel for the Revenue. We are not inclined to permit the appellants to add to the list of impugned Notifications	 now in section appeal. In their writ petitions	 the appellants did not challenge the validity of the Notification dated 28 4 51. They never raised this point before the learned 795 Single Judge. Of course	 before the appellate Bench	 an argument was addressed on this point	 but it does not appear to have been pressed. The Bench noted: "In the present appeal	 the Bengal Act as extended by SRO 615	 dated the 28th April 1951	 did not suffer from any infirmity. It is conceded by the learned Counsel for the respondent that the Central Government at the time it extended e the Bengal Act	 was competent to introduce such modification and restrictions as it thought fit. The certificate under article 133 of the Constitution was neither sought	 nor granted on any ground touching the validity of the Notification	 dated 28 4 1951. In the face of all this	 it is now too late for the appellants to commit a volte face. Accordingly	 we decline to entertain this new ground of challenge. The learned Counsel for the parties have	 more or less	 reiterated the same contentions which they had advanced in the High Court. On behalf of the appellants	 it is contended that the power of modification conferred on the Central Government by section 2 of the Laws Act is not an unfettered power of delegated legislation but a subsidiary power conferred for the limited purpose of extension and application to a Union Territory	 an enactment in force in a State. It is maintained that only such modifications are permissible in the exercise of that power which are necessary to adapt and adjust such enactment to local conditions. According to Shri Ashok Sen	 the power given by section 2 is a power of conditional legislation which is different from the power of delegated legislation. It is submitted that it is not a recurring power; it exhausts itself on extension	 and in no case this power can be used to change the basic scheme and structure of the enactment or the legislative policy ingrained in it. The submission is that the impugned notification	 dated 7 12 1957	 is bad because it has been issued more than 61 years after the extension of Bengal Act	 and it attempts to change the re rquirement of section 6(2) as to "not less than three months notice" which P is the essence of the whole provision. Reference has been made to this Court 's opinion in Re: Delhi Laws Act (supra) and the decision in Raj Narain Singh case (supra). Shri Ashok Sen further submits that by the amending Act 20 of 1959	 parliament did not put its seal of approval on the impugned notification or the changes sought to be made by it in section 6 of the Bengal Act. It is stressed that the amending Act of 1959	 did not touch section 6 at all and therefore it could not be said with any stretch of imagination	 that Parliament had referentially or impliedly incorporated or approved the purported change made by the impugned notification	 in the Bengal Act. As against the above	 Shri B. Sen	 the learned Counsel for the Revenue submits that the impugned notification does not change the essential structure or the policy embodied in section 6(2) of the Bengal Act. 796 According to Counsel	 the policy underlying section 6(2) is that reasonable notice of the Government 's intention to add to or omit anything from the Second Schedule must be given by publication in the official Gazette. It is maintained that the requirement as to "not less than three months ' notice" in the section was not a matter of policy but one of detail or expedience; it was only directory	 and the modification made by the impugned notification did not go beyond adjusting and adapting it to the local conditions of Delhi. Bengal	 it is pointed out	 is a big	 far flung State while the Territory of Delhi is a small	 compact area and therefore	 it would not be necessary or unreasonable to give a notice of less than three months for every amendment of the Schedule. Reliance has been placed on this Court 's dictum in Raza Buland Sugar Co. 's case (supra). It is argued that the power to add or omit from the Second Schedule conferred on the Government is in consonance with the accepted practice of the Legislature; that it is usual for the legislature to leave a discretion to the executive to determine details relating to the working of taxation laws	 such as the selection of persons on whom the tax is to be levied or rates at which it is to be charged in respect of different classes of goods and the like. Reference has been made to the observations of this Court in Pt.Benarsi Das Bhanot vs State of Madhya Pradesh in the context of section 6(2) of the Central Provinces and Berar Sales Tax Act 1947. Shri B. Sen further contends that the power of modification given by section 2 of the Laws Act	 does not exhaust itself on first exercise; it can be exercised even subsequently if through oversight or otherwise	 at the time of extension of the enactment the Central Government fails to adapt or modify certain provisions of the extended enactment for bringing it in accord with local conditions. In this connection support has been sought from the observations of Fazal Ali J. at p. 850 of the Report in Re: Delhi Laws Act (supra). Our attention has also been invited to section 21 of the General Clauses Act which according to Counsel	 gives power to the Central Government to add to	 amend	 vary or rescind any notification etc if the power to do so does not run counter to the policy of the legislature or affect any change in its essential features. Learned Counsel has further tried to support the reasoning of the appellate Bench of the High Court	 that whatever infirmity may have existed in the impugned notification and the modification made there by in section 6(2)	 it was rectified and cured by Parliament when it passed the Amendment Act 20 of 1959. It is urged that the Bengal Act together with the modifications made by notifications	 dated 28 4 51	 and 7 12 1957	 must have been before Parliament when it considered and passed the Amendment Act of 1959. Our attention has been invited to its preamble which is to the effect: "An Act further to amend the Bengal Finance (Sales Tax) Act	 1941	 as in force in the Union Territory of Delhi	 and also to the words as in forcer in the Union Territory of Delhi" in section 2 of the amending Act. :Reference has been made to this Court 's decisions in Venkatrao Esajirao 's case (supra)	 and Gwalior Rayon Silk Mfg.(Wvg.) Co. Ltd. The Assistant Commissioner of Sales tax and ors. 797 An alternative argument advanced by Shri B. Sen is that if in section 6(2) the requirement as to "not less than three months ' notice" was mandatory and a matter of legislative policy	 then the exemptions from tax granted to Durries	 pure silk etc.after the issue o the impugned notification must be treated non est and void ab initio	 inasmuch as the amendments of the Second Schedule whereby those exemptions were granted	 were made without complying with the requirement of not less than three months ' notice". It is argued that if this requirement was a sine qua non for amendment of the Second Schedule	 it could not be treated mandatory in one situation and directory in another. If it was mandatory then compliance with it would be absolutely necessary both for granting an exemption and withdrawing an exemption from tax. In this view of the matter	 according to Shri B. Sen	 the withdrawal of the exemption through the impugned notification was a mere formality; the notifications simply declared the withdrawal of something which did not exist in the eye of law. Appellants cannot therefore have any cause of grievance if the invalid and still born exemptions were withdrawn by the questioned notifications. In reply to this last argument	 learned Counsel for the appellants submit that this ground of defence was not pleaded by the Revenue in its affidavit before the learned Single Judge. This	 according to the Counsel	 was a question of fact which required evidence for its determination	 and was therefore required to be pleaded. Since the Respondents did not do so	 they should not have been allowed to take it for the first time at the time of arguments. Even otherwise proceeds the argument the Respondents are not competent to take this stand which is violative of the basic canon of natural justice	 according to which no party can be allowed to take advantage of its own wrong. It is stressed that the object of the requirement of not less than three months ' notice	 was to afford an opportunity to persons likely to be adversely affected to raise objections against the proposed withdrawal or curtailment of an exemption from tax. That being the case	 only the persons aggrieved could have the necessary locus standi to complain of a non compliance with this requirement. In Re: Delhi Laws (supra) this Court inter alia examined the constitutional validity of section 2 of the Laws Act in the light of general principles relating to the nature	 scope and limits of delegated legislation. Section 2 as it then stood	 was as follows: "The Central Government may	 by notification in the official Gazette	 extend to any Part State (other than Coorg and the Andaman and Nicobar Islands) or to any part of such State with such restrictions and modifications as it thinks fit any enactment which is in force in a Part A State at the date of the notification and provision may be made in any enactment so extended for the repeal or amendments of any corresponding law (other than a Central Act) which is for the time being applicable to that Part State. " The Court by a majority held that the first part of this section which empowers the Central Government to extend to any Part State or to any part of such State with such modifications and restrictions as it 798 thinks fit any enactment which is in force in a Part A State	 is intra vires	 and that the latter part of this section which empowers the Central Government to make provision in any enactment extended to a Part State	 for repeal or amendment of any law (other than a Central Act) which is for the time being applicable to that Part State	 is ultra vires. Consequent upon this opinion	 the latter part of the section was deleted by section 3 of the Repealing and Amending Act	 195 (Act XLVIlI of 1952) with effect from 2 8 1951. The majority opinion in upholding the validity of the first portion of section 2 of the Laws Act drew a good deal from the observations of the Privy Council in Queen vs Burah wherein it was said: "If what has been done is legislation within the general scope of the affirmative words which give the power and if it violates no express condition or restrictions by which that power is limited. it is not for any court of justice to enquire further or to enlarge constructively those conditions and restrictions". "Where plenary powers of legislation exist as to particular subjects	 whether in an Imperial or in a Provincial Legislature	 they may (in their Lordships judgment) be well exercised	 either absolutely or conditionally. Legislation conditional on the use of particular powers	 or on the exercise of a limited discretion	 entrusted by the legislature to persons in whom it places confidence	 is no uncommon thing; and	 in any circumstances it may be highly convenient." (emphasis supplies) Before proceeding further	 it will be proper to say a few words in regard to the argument that the power conferred by section 2 of the Laws Act is a power of conditional legislation and not a power of delegated legislation. In our opinion	 no useful purpose will be served to pursue this line of argument because the distinction propounded between the two categories of legislative powers makes no difference	 in principle. In either case	 the person to whom the power is entrusted can do nothing beyond the limits which circumscribe the power; he has to act to use the words of Lord Selborne "within the general scope of the affirmative words which give the power" and without violating any "express conditions or restrictions by which that power is limited". There is no magic in a name. Whether you call it the power of "conditional legislation" as Privy Council called it in Burah 's case (supra) or 'ancillary legislation ' as the Federal Court termed it in Choitram vs Commissioner of Income tax	 Bihar or 'subsidiary legislation ' as Kania C.J. styled	 it or whether you camouflage it under the veiling name of 'administrative or quasi legislative power ' as Professor Cushman and other authorities have done it necessary for 799 bringing into operation and effect an enactment	 the fact remains that it has a content	 howsoever small and restricted of the law making power itself. There is ample authority in support of the proposition that the power to extend and carry into operation an enactment with necessary modifications and adaptations is in truth and reality in the nature of a power of delegated legislation. In Re: Delhi Laws Act (supra) S.R. Das J. said that on strict analysis it was "nothing but a delegation of a fractional legislative power". Anglin J. in Grays case regarded this what is called conditional legislation ' as "a very common instance of limited delegation. More or less to the same effect is the view taken by Evatt J. of Australia in Dignams case. Prof. Kennedy (vide his treatise 'Constitution of Canada '	 2nd Edn.p. 463)	 is also of opinion that 'conditional legislation ' is "a form of delegation". We do not want to multiply authorities nor wish to carry this academic discussion to a final conclusion because it is not necessary for solution of the problem in hand. In the instant case	 the precise question with which we are faced is whether the purported substitution of the words "such previous notice as is considers reasonable" for the words "not less than three months notice" in section 6(2) by the impugned notification dated 7th December	 1957	 was in excess of the power of 'modification ' conferred on the Central Government by section 2 of the Laws Act. This question has to be answered in the light of the principles enunciated by this Court in Re: Delhi Laws Act relating to the nature and scope of this power. Out of the majority who upheld the validity of this provision of section 2 of the Laws Act	 with which we are concerned	 Fazal Ali J. explained the scope of the words "much modifications as it thinks fit" in section 2	 thus: "These are not unfamiliar words and they are often used by careful draftsmen to enable laws which are applicable to one place or object to be so adapted as to apply to another. The power of introducing necessary restrictions and modifications is incidental to the power to apply or adapt the law	 and in the context in which the provision as to modification occurs it cannot bear the sinister sense attributed to it. The modifications are to be made within the framework of the Act and they cannot be such as to affect its identity or structure or the essential purposes to be served by it. The power to modify certainly involves a discretion to make suitable changes	 but it would be useless to give an authority the power to adapt a law without giving it the power to make suitable changes." Vivian Bose J. also observed in a similar strain	 at p. 1124; 800 "The power to "restrict and modify" does not import the power to make essential changes. It is confined to alterations of a minor character such as are necessary to make an Act intended for one area applicable to another and to bring it into harmony with laws already in being in the State	 or to delete portions which are meant solely for another area. To alter the essential character of an Act or to change it in material particulars is to legislate	 and that	 namely	 the power to legislate	 all authorities are agreed	 cannot be delegated by a legislature which is not unfettered." Mukherjea J. was of the view that the "essential legislative function" which consists in the determination or choosing of the legislative policy and of formally enacting that policy into a "binding rule of conduct" cannot be delegated. Dealing with the construction of the words "restrictions" and "modification" in the Laws Act	 the learned Judge said" at pages 1004 10O6: "The word "restrictions" . connotes limitation imposed on a particular provision so as to restrain its application or limit its scope	 it does not by any means involve any change in the principle. It seems to me that in the context and used alongwith the word "restriction" the word " 'modification" has been employed also in a cognate sense	 and it does not involve any material or substantial alteration. The dictionary meaning of the expression "to modify" is to "tone down" or to "soften true rigidity	 of the thing" or "to make partial changes without any radical alteration". It would be quite reasonable to hold that the word "modification" in section 7 of the Delhi Laws Act (which is almost identical with the present section 2	 Laws Act) means and signifies changes of such character as are necessary to make the statute which is sought to be extended able to the local conditions of the province. I do not think that the executive Government is entitled to change the whole nature or policy underlying any particular Act or to take different portions from different statutes and prepare what has been described before us as "amalgam" of several laws. these things would be beyond the scope of the section itself." (emphasis supplied). S.R. Das J. (as he then was) delineated the scope of the power of "modification" given under section 7 of the (for short the Delhi Act) at p. 1089 as follows: "It may well be argued that the intention of section 7 of the was that the permissible modifications were to be such as would	 after modification	 leave the general character of the enactment intact. One of the meanings of the word "modify" is given in the oxford Dictionary Vol.I	 page 1269 as "to alter without radical transformation". If this meaning is given to the word "modification" in section 7 of the then the modifications contemplated 801 thereby were nothing more than adaptations which were included in the expressions mutatis mutandis and the "restrictions	 limitations or proviso" mentioned in the several instances of conditional legislation referred to by the Privy Council (in Burah 's case). It is to be noted that the language of s.7 of the Delhi Act was substantially the same as that of the first portion of section 2 of the Part C State Laws Act	 as it then stood. What Das J. said about the scope of "restrictions and modifications" in the context of section 7 of the Delhi Act substantially applies to the ambit and meaning of these words occurring in section 2 of the Laws Act. Again	 in Rajnarainsingh 's case (supra)	 Vivian Bose J. speaking for the Court	 summed up the majority view in regard to the nature and scope of delegated legislation in Re: Delhi Laws (supra)	 thus: "In our opinion the majority view was that an executive authority can be authorised to modify either existing or future laws but not in any essential feature. Exactly what constitutes an essential feature cannot be enunciated in general terms	 and there was some divergence of view about this in the former case	 but this much is clear from the opinions set out above: it cannot include a change of policy". Bearing in mind the principles and the scope and meaning of the expression "restrictions and modifications" explained in 	 let us now have a close look at section 2. It will be clear that the primary power bestowed by the section on the Central Government	 is one of extension	 that is	 bringing into operation and effect	 in a Union Territory	 an enactment already in force in a State. The discretion conferred by the Section to make 'restrictions and modifications ' in the enactment sought to be extended	 is not a separate and independent power. It is an integral constituent of the powers of extension. It cannot be exercised apart from the power of extension. This is indubitably clear from the preposition "with" which immediately precedes the phrase "such restrictions and modifications" and conjoins it to the principal clause of the section which gives the power of extension. According to the Shorter Oxford Dictionary	 one meaning of the word "with"	 (which accords here with the context)	 is "part of the same whole". The power given by section 2 exhausts itself on extension of the enactment; it cannot be exercised repeatedly or subsequently to such extension. It can be exercised only once	 simultaneously with the extension of the enactment. This is one dimension of the statutory limits which circumscribe the power. The second is that the power cannot be used for a purpose other than that of extension. In the exercise of this power	 only such "restrictions and modifications" can be validly engrafted in the enactment sought to be extended	 which are necessary to bring it into operation and effect in the Union Territory. "Modifications" which are not necessary for	 or ancillary and subservient to the purpose 802 of extension	 are not permissible. And	 only such "modifications" can be legitimately necessary for such purpose as are required to adjust	 adapt and make the enactment suitable to the peculiar local conditions of the Union Territory for carrying it into operation and effect. In the context of the section	 the words "restrictions and modifications" do not cover such alterations as involve a change in any essential feature	 of the enactment or the legislative policy built into it. This is the third dimension of the limits that circumscribe the power. It is true that the word "such restrictions and modifications as it thinks fit"	 if construed literally and in isolation	 appear to give unfettered power of amending and modifying the enactment sought to be extended. Such a wide construction must be eschewed lest the very validity of the section becomes vulnerable on account of the vice of excessive delegation. Moreover	 such a construction would be repugnant to the context and the content of the section	 read as a whole	 and the statutory limits and conditions attaching to the exercise of the power. We must	 therefore	 confine the scope of the words "restrictions and modifications" to alterations of such a character which keep the inbuilt policy	 essence and substance of the enactment sought to be extended	 intact	 and introduce only such peripheral or insubstantial changes which are appropriate and necessary to adapt and adjust it to the local conditions of the Union Territory. The impugned notification	 dated 7 12 1957	 transgresses the limits which circumscribe the scope and exercise of the power conferred by section 2 of the Laws Act	 at least	 in two respects. Firstly	 the power has not been exercised contemporaneously with the extension or for the purposes of the extension of the Bengal Act to Delhi. The power given by section 2 of the Laws Act had exhausted itself when the Bengal Act was extended	 with some alterations	 to Delhi by Notification dated 28 4 1951. The impugned notification has been issued on 7 12 1957	 more than 6 1/2 years after the extension. There is nothing in the opinion of this Court rendered in Re: (supra) to support Mr. B. Sen 's contention that the power given by section 2 could be validly exercised within one year after the extension. What appears in the opinion of Fazl Ali J. at page 850	 is merely a quotation from the report of the Committee on Minister 's Powers which considered the propriety of the legislative practice of inserting a "Removal of Difficulty Clause" in Acts of British Parliament	 empowering the executive to modify the Act itself so far as necessary for bringing it into operation. This device was adversely commented upon. While some critics conceded that this device is "partly a draftsman 's insurance policy	 in case he has overlooked something" (e.g. Sir Thomas Carr	 page 44 of his book "Concerning English Administrative Law")	 others frowned upon it	 and nicknamed it as "Henry VIII Clause" after the British Monarch who was a notorious personification of absolute despotism. It was in this perspective that the Committee on Minister 's Powers examined this practice and recommended: 803 ". first	 that the adoption of such a clause ought on each occasion when it is	 on the initiative of the Minister in charge of the Bill	 proposed to Parliament to be justified by him upto the essential. It can only be essential for the limited purpose of bringing an Act into operation and it should accordingly be in most precise language restricted to those purely machinery arrangements vitally requisite for that purpose; and the clause should always contain a maximum time limit of one year after which the power should lapse". It may be seen that the time limit of one year within which the power under a Henry VIII Clause should be exercisable	 was only a recommendation	 and is not an inherent attribute of such power. In one sense	 the power of extension cum modification given under section 2 of the Laws Act and the power of modification and adaptation conferred under a usual 'Henry VIII Clause	 ' are kindred powers of fractional legislation	 delegated by the legislature within narrow circumscribed limits. But there is one significant difference between the two. While the power under section 2 can be exercised only once when the Act is extended	 that under a 'Henry VIII Clause ' can be invoked	 if there is nothing to the contrary in the clause more than once	 on the arising of a difficulty when the Act is operative. That is to say	 the power under such a Clause can be exercised whenever a difficulty arises in the working of the Act after its enforcement	 subject of course to the time limit	 if any	 for its exercise specified in the statute. Thus	 anything said in Re: (supra)	 in regard to the time limit for the exercise of power under a 'Henry VIII Clause '	 does not hold good in the case of the power given by section 2 of the Laws Act. Fazl Ali J.	 did not say anything indicating that the power in question can be exercised within one year of the extension. On the contrary	 the learned Judge expressed in unequivocal terms	 at page 849: "Once the Act became operative any defect in its provision cannot be removed until amending legislation is passed." Secondly	 the alteration sought to be introduced by this Notification (7 12 1957) in section 6(2)	 goes beyond the scope of the 'restrictions and modifications ' permissible under section 2 of the Laws Act; it purports to change the essential features of sub section (2) of section 6. and the legislative policy inherent therein. Section 6(2)	 as it stood immediately before the impugned notification	 requires the State Government to give by Notification in the Official Gazette "not less than 3 months notice" of its intention to add to or omit from or otherwise amend the Second Schedule. The primary key to the problem whether a statutory provision is mandatory or directory	 is the intention of the law maker as expressed in the law	 itself. The reason behind the provision may be a further aid to the ascertainment of that intention. If the legislative intent is expressed clearly and strongly in imperative words	 such as the use of 'must ' instead of "shall"	 that will itself be sufficient to hold 804 the provision to be mandatory	 and it will not be necessary to pursue the enquiry further. If the provision is couched in prohibitive or negative language	 it can rarely be directory	 the use of peremptory language in a negative form is per se indicative of the intent that the provision is to be mandatory (Crawford	 the Construction of Statutes pp.523 24). Here the language of sub section (2) of section 6 is emphatically prohibitive	 it commands the Government in unambiguous negative terms that the period of the requisite notice must not be less than three months. In fixing this period of notice in mandatory terms	 the legislature had	 it seems taken into consideration several factors. According to the scheme of the Bengal Act	 the tax is quantified and assessed on the quarterly turnover. The period of not less than three months notice conforms to that scheme and is intended to ensure that imposition of a new burden or exemption from tax causes least dislocation and inconvenience to the dealer in collecting the tax for the Government	 keeping accounts and filing a proper return	 and to the Revenue in assessing and collecting the same. Another object of this provision is that the public at large and the purchasers on whom the incidence of the tax really falls	 should have adequate notice of taxable items. The third object seems to be that the dealers and others likely to be affected by an amendment of the Second Schedule may get sufficient time and opportunity for making representations	 objections or suggestions in respect of the intended amendment. The dealers have also been ensured adequate time to arrange their sales adjust their affairs and to get themselves registered or get their licenses amended and brought in accord with the new imposition or exemption. Taking into consideration all these matters	 the legislature has in its judgment solemnly incorporated in the statute	 fixed the period of the requisite notice as "not less than three months" and willed this obligation to be absolute. The span of notice was thus the essence of the legislative mandate. The necessity of notice and the span of notice both are integral to the scheme of the provision. The sub section cannot therefore be split up into essential and non essential components	 the whole of it being mandatory. The rule in Raza Buland Sugar Co. 's case (supra) has therefore no application. Thus section 6(2) embodies a determination of legislative policy and its formulation as an absolute rule of conduct which could be diluted	 changed or amended only by the legislature in the exercise of its essential legislative function which could not	 as held in Re: (supra) and Rajnarainsingh 's case (supra) be delegated to the Government. For these reasons we are of opinion that the learned single Judge of the High Court was right in holding that the impugned notification was outside the authority of the Central Government as a delegate under section 2 of the Laws Act. Before proceeding further	 we may mention here in passing that the point for decision in Benarsi Das Bhanot 's case (supra) relied on by the Division Bench of the High Court	 was different from the one 805 before us. There	 the constitutional validity of section 6(2) of the Central Provinces and Berar Sales Tax Act	 1947	 was questioned on the ground of excessive delegation. In the instant case the validity of section 6(2) of the Bengal Act	 as such is not being impeached. There is yet another facet of the matter. By the impugned notification	 the Central Government did not directly seek to amend section 6(2). Perhaps it was not sure of its competence to do so more than 6 1/2 years after the extension of Bengal Act to Delhi. It therefore chose to amend section 6(2) indirectly through the amendment of its earlier notification dated 28 4 51	 which was only a vehicle or instrument meant for extension of the Bengal Act to Delhi. On such extension	 the notification had exhausted its purpose and had spent its force. It had lost its utility altogether as an instrument for modification of the Bengal Act. Therefore	 the issue of the impugned notification which purported to amend section 6(2) through the medium of a "dead" notification	 was an exercise in futility. In any case	 an amendment which was not directly permissible could not be indirectly smuggled in through the back door. We now turn to the main ground on which the judgment of the appellate Bench of the High Court rests. The question is	 was the invalidity from which the impugned notification	 dated 7 12 1957	 suffered cured by the Amendment Act of 1959 ? The Bench seems to think that by passing this Amendment Act	 Parliament had put its seal of approval on the Bengal Act as it stood extended and amended by the Notifications of 1957 and 1957. We find no basis for this surmise. This Amendment Act leaves section 6(2) untouched; it does not even indirectly	 refer to the impugned notification or the amendment purportedly made by it in section 6(2). Nor does it re enact or validate what was sought to be achieved by the impugned Notification. No indication of referential incorporation or validation of the impugned notification or the amendment sought to be made by it	 is available either in the preamble or in any other provision of the Amendment Act. In Krishna Chandra vs Union of India	(1) relied upon by the learned Counsel for the Respondents	 the central issue for consideration was	 whether R. 20(2) framed by the Bihar Government under section 15 of the and the second proviso to section 10(2) of the Bihar Land Reforms Act	 1950 were constitutionally valid. By the combined operation of these statutory provisions	 the petitioners therein were called upon to pay certain rent and royalties in respect of mining operations. Those demands were challenged in Baijnath Kedia vs State of Bihar(2) wherein this Court held that the Bihar legislature had no jurisdiction to enact the second proviso to section 10(2) of the Bihar Act because section 15 of the Central Act	 read with section 2 thereof	 had appropriated the whole field relating to mining minerals for Parliamentary legislation. The upshot of that decision was	 that the action taken by the 806 Bihar Government in modifying the terms and conditions of the leases which were in existence anterior to the Rules and the levy sought to be made on the strength of the amended Bihar Act and Rule	 were unsustainable. Thereupon the State persuaded Parliament to enact the Validation Act of 1969 with a view to remove the road blocks which resulted in the decision in Kedia 's case (supra). Section 2 of the Validation Act runs thus: "Validation of certain Bihar State laws and action taken and things done connected therewith. (1) The laws specified in the Schedule shall be and shall be deemed always to have been	 as valid as if the provisions contained therein had been enacted by Parliament. (2) Notwithstanding any judgment	 decree or order of any court	 all actions taken	 things done	 rules made	 notification issued or purported to have been taken	 done	 made or issued and rents or royalties realised under any such laws shall be deemed to have been validly taken	 done	 made	 issued or realised	 as the case may be	 as if this section had been in force at all material times when such action was taken	 things were done	 rules were made	 notifications were issued	 or rents or royalties were realised	 and no suit or other proceeding shall be maintained or continued in any court for the refund of rents or royalties realised under any such laws. (3) For the removal of doubts	 it is hereby declared that nothing in sub section (2) shall be construed as preventing any person from claiming refund of any rents or royalties paid by him in excess of the amount due from him under any such laws. " The precise question before the Court was	 whether a statute or a rule earlier declared by the Court to be unconstitutional or otherwise invalid can be retroactive through fresh validating legislation enacted by the competent legislature. Answering this question in the affirmative	 this Court	 speaking through Krishna Iyer	 J. observed: "where Parliament having power to enact on a topic actually legislates within its competence but	 as an abbreviation of drafting	 borrows into the statute by reference the words of a State Act not qua State Act but as a convenient shorthand	 as against a longhand writing of all the sections into the Central Act	 such legislation stands or falls on Parliament 's legislative power	 vis a vis the subject viz.	 mines and minerals. The distinction between the two legal lines may sometimes be fine but always is real. 807 If Parliament has the power to legislative on the topic	 it can make an Act on the topic by any drafting means	 including by referential legislation." "Taking a total view of the circumstances of the Validation Act Parliament did more than simply validate an invalid law passed by the Bihar Legislature but did reenact it with retrospective effect in its own right adding an amending Central Act to the statute book. " The position in the instant case is entirely different. Here	 Parliament despite its presumed awareness of the impugned Notification	 has said nothing in the Amending Act of 1959	 indicating that it (Parliament) has by 'longhand ' or 'shorthand ' method incorporated	 re enacted or validated the impugned notification or the amendment sought to be made thereby	 while passing the Amendment Act	 1959. The appellate Bench was therefore in error in holding that Parliament had validated or re enacted referentially with retrospective effect what was sought to be done by the impugned notification	 when it passed the Amending Act	 1959. The High Court has tried with the aid of this Court 's decision in Venkatrao vs State of Bombay (supra) to spell out the proposition that mere amendment of an Act by a competent legislature	 amounts to re enactment of the parent Act. We find nothing in this Court 's decision in Venkatrao 's case which warrants the enunciation of such a sweeping rule. All that was decided in Venkatrao 's case was that the assent given by the President to the Amending Act would be deemed to be an assent accorded to the parent Act	 also. The decision in Venkatrao 's case therefore does not advance the case of Shri B. Sen. Shri B. Sen 's alternative argument that the notifications whereby the exemptions from tax have been withdrawn in regard to Durries	 pure silk	 country liquor etc. are not assailable because those exemptions were earlier granted without giving three months ' notice	 is manifestly unsustainable. Firstly	 so far as fruits	 fresh and dried (item 8)	 Pepper	 tamarind and chillies (item 11)	 Turmeric (item 14)	 ghee (item 16)	 and knitting wool	 (item 21A) are concerned	 they were exempted goods in the Schedule of the Bengal Act	 as modified and extended by the Notification	 dated 28 4 1951	 to Delhi. No question of giving notice for granting these exemptions therefore arose. Secondly	 the validity of the notifications whereby exemptions were granted to pure silk	 liquor etc.after the extension of the Bengal Act to Delhi is not in issue. This plea was not set up by the Respondents in their affidavits. Whether or not notice for the requisite period was given before issuing the exemption notifications	 was a question of fact depending on evidence. Thirdly	 to allow the Respondents to take their stand on such a plea would be violative of the fundamental principle of natural justice	 according to which	 a party cannot be allowed to take advantage of its own lapse or wrong. The statute 808 has imposed a peremptory duty on the Government to issue notice of not less than three months	 of its intention to amend the Second Schedule. It therefore cannot be allowed to urge that since it had disobeyed this mandate on an earlier occasion when it granted the exemptions it can withdraw the exemptions in the same unlawful mode. Two wrongs never make a right. Nor could the Respondents derive any authority or validity from section 21 of the General Clauses Act	 for the notifications withdrawing the exemptions. The source from which the power to amend the Second Schedule	 comes is section 6(2) of the Bengal Act and not section 21 of the General Clauses Act. Section 21	 as pointed out by this Court in Gopichand vs Delhi Administration(1) embodies only a rule of construction and the nature and extent of its application must be governed by the relevant statute which confers the power to issue the notification. The power therefore had to be exercised within the limits circumscribed by section 6(2) and for the purpose for which it was conferred. For all the foregoing reasons	 we are of opinion that the impugned notification	 dated 7 12 1957	 purporting to substitute the words "such previous notice as it considers reasonable" for the words "not less than three months notice" in section 6(2) of the Bengal Act is beyond the powers of the Central Government	 conferred on it by section 2 of the Laws Act. In consequence	 the notification dated 1 4 1958	 19 9 1959	 29 6 1966 and 31 7 1970 in so far as they withdrew the exemptions from tax in the case of Durries	 pure silk	 country liquor	 kirayana articles etc.were withdrawn without complying with the mandatory requirement of not less than three months notice enjoined by section 6(2) of the Bengal Act	 are also invalid and ineffective. In the result we allow these appeals	 set aside the judgment of the appellate Bench of the High Court and declare the Notification dated 7 12 1957	 and the subsequent notifications in so far as they withdrew the exemptions from tax	 mentioned above	 to be unconstitutional. In the circumstances of the case	 we leave the parties to bear their own costs. V.P.S. Appeals allowed.

Section 2 of the Part States (Laws) Act	 1950	 empowered the Central Government to extend by notification in the official gazette	 to any Part C State	 or to any part of it	 with such restrictions and modifications as it thinks fit	 any enactment in force in a Part A State. In 1951	 the Central Government	 in exercise of this power	 extended by a Notification the Bengal Finance (Sales Tax) Act	 1941	 to the then Part State of Delhi with certain modifications in section 6. The section	 after such extension with modifications	 provided: 6(1) No tax shall be payable under this Act on the sale of goods specified in the first column of the Schedule subject to the conditions etc: and (2) The State Government [Amended as Central Government in 1956] after giving by notification in the official gazette not less than 3 months notice of its intention to do so	 may by like notification add to or omit from or otherwise amend the Schedule and thereupon the Schedule shall he amended accordingly A modified Schedule of goods exempted from tax under section 6 was also substituted for the original Schedule in the Bengal Act	 by the Notification. After the passing of the 	 the Part States (Laws) Act became . with necessary adaptations. In 1957	 the Central Government issued a Notification in purported exercise of the powers under section 2 of the 1950 Act	 amending the 1951 Notification. By the 1957 Notification an additional modification of section 6 of the Bengal Act was introduced in the 1951 Notification	 namely the words "such previous notice as it considers reasonable" were substituted for the words "not less than 3 months ' notice" in section 6(2). In 1959	 Parliament passed the Bengal (Sales Tax) (Delhi Amendment) Act	 1959	 making some amendments in various sections of the Bengal Act but left section 6 untouched. By various notifications	 exemption from sales tax was granted to several commodities. but subsequently	 the exemption was withdrawn by other notifications after giving notice of less than 3 months. Dealers in those commodities	 who were aggrieved by the withdrawal of the exemption	 challenged the validity of ' the withdrawal. The High Court dismissed their petitions. On the main ground that Parliament	 while enacting the Amending Act of 1959	 had put its seal of approval to the curtailed period of notice in section 6(2) and as such	 it should be taken to have keen provided by Parliament itself in the Bengal Act. 786 Allowing the appeals to this Court	 ^ HELD: The 1957 Notification purporting to substitute the words "such previous notice as it considers reasonable" for the words 'not less than 3 months ' notice" in section 6(2) of the Bengal Act	 is beyond the powers of the Central Government	 conferred on it	 by section 2 of the ; and in consequence	 the various notifications	 in so far as they with drew exemptions from tax with respect to the several commodities	 are invalid and ineffective	 as the exemption was withdrawn without complying with the mandatory requirement of not less than 3 months ' notice enjoined by the section. [808 D E] (1) (a) The primary power bestowed by section 2 of the 	 on the Central Government is one of extension	 that is	 bringing into operation and effect	 in a Union Territory	 an enactment already in force in a State. The discretion conferred by the section to make "restrictions and modifications" in the enactment sought to be extended	 is not a separate and independent power	 which can be exercised apart from the power of extension	 but is an integral constituent of the power of extension. This is made clear by the use of the preposition "with" one meaning of which (which accords with the context) is "part of the same whole". [801 E F] (b) There are 3 limits on the power given by section 2. (i) The power exhausts itself on extension of the enactment. It can be exercised only once	 simultaneously with the extension of the enactment	 but cannot be exercised repeatedly or subsequently to such extension. (ii) The power cannot be used for a purpose other than that of extension. In the exercise of the power	 only such restrictions and modifications can be validly engrafted in the enactment sought to be extended	 which are necessary to bring it into operation and effect in the Union Territory. Modifications which are not necessary for	 or ancillary and subservient to the purpose of extension	 are not permissible. Only such modifications can be legitimately necessary for such purpose	 as are required to adjust	 adapt	 and make the enactment suitable to the peculiar local conditions of the Union Territory for carrying it into operation and effect. (iii) The words "restrictions and modifications" do not cover such alterations as involve a change in any essential feature of the enactment or the legislative policy built into it. [801G H	 802A] (c) If the words "such restrictions and modifications as it thinks fit" are given the wide construction of giving an unfettered power of amending and modifying the enactment sought to be extended	 as contended by the respondent	 the validity of the section itself becomes vulnerable on account of the vice of excessive delegation. Moreover. such a construction would be repugnant to the context and content of the section	 read as a whole. [802 B C] Rajnarain Singh vs The Chairman Patna Administration Committee Patna and Re: Delhi Laws Act; 	 	 referred to. (2) The 1957 Notification transgresses these limits in two respects : (a) The power has not been exercised contemporaneously with the extension or for the purposes of the extension of the Bengal Act to Delhi but 6.6 years thereafter. The power of extension with restrictions and modifications had exhausted itself when the Bengal Act was extended to Delhi with some alterations by the 1951 Notification. [802D E] The power given under section 2 of the 1950 Act	 cannot be equated to the "Henry VIII clause" of the Acts of the British Parliament because while the power under section 2 can be exercised only once when the Act is extended	 the power under a "Henry VIII clause" can be invoked	 if there is nothing contrary in the clause	 more than once on the arising of a difficulty when the Act is operative [802F H] Observations of Fazal Ali	 J. at p. 850 in Re: Delhi Laws Act case explained. 787 (b) The alteration sought to be introduced in section 6(2) by the 1957 Notification goes beyond the scope of the "restrictions and modifications" permissible under section 2 of the 1950 Act	 because	 it purports to change the essential features of section 6(2) and the legislative policy inherent therein. [803F] Section 6(2) before the issue of the 1957 Notification	 requiring the Government to give "not less than 3 months ' notice" of its intention to add to or omit from or otherwise amend the Schedule to the 1950 Act	 embodies a determination of legislative policy and its formulation as an absolute rule of ' conduct could be diluted	 changed or amended only by the legislature	 in the exercise of its essential legislative function	 which could not be delegated to the Government. [803G 804E	 F	 G] (i) The language of the sub section as it stood is emphatically prohibitive and it commands the Government in unambiguous negative terms that the period of the requisite notice must not be less than 3 months	 showing that the provision was mandatory and not directory. [804 A B] (ii) The scheme of the Bengal Act is that the tax is to be quantified and assessed on the quarterly turnover. and the period of not less than 3 months	 notice conforms to the scheme and ensures that the imposition of a new tax of exemption does not cause dislocation or inconvenience either to the dealer or the Revenue. [804B] (iii) By fixing the period at not less than 3 months	 purchasers on whom the incidence of tax really falls have adequate notice of taxable items. [804 C] (iv) Dealers and others likely to be affected by an amendment of the Schedule get sufficient time to make representations and adjust their affairs. [804 D] The span of notice was thus the essence of the legislative mandate. The necessity of notice and the span of notice both are integral to the scheme of the provision and it cannot be split up into essential and non essential components	 the whole of it being mandatory. [804 E F] Raza Buland Sugar Co. Ltd. vs Municipal Board	 Rampur	 ; 	 distinguished. (3)(a) Pt. Benarsi Das Bhanot vs State of Madhya Pradesh does not assist the respondent. That was a case where the contention that 5. 6(2) of the C.P. & Bihar Sales Tax Act	 1947	 was invalid on the ground of excessive delegation	 was rejected	 by the Court. In the present case	 it is the validity of a Notification purported to be issued under section 2 of the 1950 Act that is impeached as beyond the powers of modification conferred by the section. [804H	 805A] (b) In the present case	 the Central Government did not directly amend section 6(2). More than 6 years after the extension of the Act by the 1951 Notification	 it amended the sub section indirectly by amending the 1951 Notification. But on the extension of the Act to Delhi	 the 1951 Notification had exhausted its purpose	 and the purported amendment	 through the medium of such a "dead" Notification is an exercise in utility. Further	 an amendment which was not directly permissible could not be done indirectly. [805 B	 C] (4) The High Court was in error in holding that Parliament had validated or re enacted referentially	 with retroactive effect	 what was sought to be done by the 1957 Notification when it passed the Amending Act	 1959. [807C] The Amending Act leaves section 6(2) untouched. It does not even indirectly refer to the 1957 Notification or the amendment purportedly made by it in section 6(2). Nor does it re enact or validate what was sought to be achieved by that notification. No indication of referential incorporation or validation of the 1957 Notification or the amendment sought to be made by it	 is available either in the Preamble or in any other provision of the Amending Act. Parliament despite its presumed awareness of the 1957 Notification	 has said nothing in the Amending Act indicating that it has in any manner incorporated	 re enacted or 788 validated the 1957 Notification or the amendment sought to be made thereby	 while passing the Amending Act	 1959. [805 E F	 807 B C] Krishna Chandra vs Union of India	 A.I.R. 1975 S.C. 1389	 referred to	 (5) A mere amendment of an Act by a competent legislature does not amount to re enactment of the parent Act. [807D] Venkatarao Esajirao Limberkar 's case [1970] 1 S.C.R. 317	 explained. (6) The respondent cannot contend that if the withdrawal of exemption without giving 3 months" notice was illegal	 then the grant of exemption without giving 3 months ' notice was also void. [808 A] (a) Some of the goods were granted exemption by the 1951 Notification itself and	 hence	 there is no question of giving notice for giving those exemptions. [807 G] (b) The validity of the notifications granting exemptions after the extension of the Act to Delhi is not in issue in the writ petitions. and whether or not the requisite notice was given before granting exemption is a question of fact depending on evidence. [807G] (c) To allow the respondent to take such a plea would be violative of the fundamental principle of natural justice	 according to which a party cannot be allowed to take advantage of his own lapse or wrong. [807 H] (7) The respondent cannot also rely on section 21 of the General Clauses Act	 because	 the source of the power to amend the Schedule to the 1950 Act. is section 6(2) of the Bengal Act and not section 21 of the General Clauses Act	 and the power has to be exercised within the limits of section 6(2) and for the purpose for which it we conferred. [808 B] Gopichand vs Delhi Administration	 [1959] Suppl. 2 S.C.R. 87	 referred to.