EXHIBIT 10.23c
                                                            EXHIBIT 10.24a


                           INSTRUMENT OF ASSUMPTION OF
                               STOCK OPTION PLANS

         This  Instrument of Assumption  of Stock  Options (the  "Instrument  of
Assumption"),  made  as  of  the  21st  day  of  July,  2000,  by  UIL  Holdings
Corporation,   a  Connecticut   corporation  ("UIL")  in  favor  of  The  United
Illuminating Company, a Connecticut corporation ("UI"),

                               WITNESSETH THAT:

         WHEREAS,  effective  at the close of  business  on July 20,  2000,  and
pursuant  to an  Agreement  and Plan of Merger and Share  Exchange,  dated as of
January  24,  2000,  among  UIL,  UI and  United  Mergings,  Inc.,  UI  became a
wholly-owned  subsidiary of UIL, and each outstanding share of UI's Common Stock
was  automatically  converted  into and  exchanged for one share of UIL's Common
Stock; and

         WHEREAS,  UI has had in effect  since  January  22,  1990 a 1990  Stock
Option Plan for certain of its key employees, which Plan, as amended immediately
prior to the  close of  business  on the 20th day of July,  2000,  includes  the
following  provision:  "In the event of any  reorganization  in which all of the
shares of the  Company's  Common  Stock are  exchanged  for shares of the common
stock  of  another   corporation,   all  Stock  Options  granted  hereunder  and
outstanding on the effective  date of the share exchange shall be  automatically
converted  into stock  options to purchase  shares of the other  corporation  on
identical terms, and the other corporation shall assume this Plan, and the Board
of Directors of the other  corporation,  excluding  any member of said Board who
is, or within twelve (12) months prior to the exercise of any  discretion  under
this Plan, has been an employee of the other corporation, its subsidiaries,  the
Company or its Subsidiaries,  shall become the Administrator of this Plan on the
effective date of the share exchange."; and

         WHEREAS, UI has had in effect since March 22, 1999, a 1999 Stock Option
Plan,  which  Plan  includes  the  following  provision:  "In the  event  of any
reorganization  in which all of the  shares of the  Company's  Common  Stock are
exchanged  for shares of the  common  stock of  another  corporation,  all Stock
Options  granted  hereunder and  outstanding  on the effective date of the share
exchange shall be automatically  converted into stock options and reload options
to purchase shares of the other  corporation on identical  terms,  and the other
corporation  shall  assume this Plan,  and the Board of  Directors  of the other
corporation,  excluding  any member of said Board who is, or within  twelve (12)
months  prior to the  exercise of any  discretion  under this Plan has been,  an
employee  of  the  other  corporation,  its  subsidiaries,  the  Company  or its
Subsidiaries,  shall become the Administrator of this Plan on the effective date
of the share exchange."

         NOW  THEREFORE,   in   consideration   of  the  premises,   UIL  hereby
acknowledges  that it has assumed and become  responsible for the performance of
all of the terms, conditions,  covenants and agreements of each of the aforesaid
Stock Option Plans on the part of UI thereunder,  including, without limitation,
the obligation to issue shares of

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Common Stock of UIL upon the exercise of Stock  Options (as that term is defined
in said Stock Option  Plans),  pursuant to and in accordance  with the terms and
conditions of said Stock Option Plans; and UIL does hereby covenant and agree to
hold harmless UI from and against any claims, demands,  suits, actions,  damages
or expenses,  including but not limited to attorneys' fees, arising out of or in
any way connected with any default or alleged  default on the part of UIL in the
faithful  performance  of  the  terms,  conditions,   covenants  and  agreements
contained in said Stock Option Plans.

         This  Instrument  of  Assumption  shall be governed by and construed in
accordance with the laws of the State of Connecticut.

         IN WITNESS WHEREOF,  UIL has caused this Instrument of Assumption to be
executed as of the day and year first above written.


UIL HOLDINGS CORPORATION


By:      s/s Robert L. Fiscus
    ------------------------------------------------
    Robert L. Fiscus
    Its Vice Chairman of the Board of Directors,
    Chief Financial Officer, Treasurer and Secretary



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