That applies in particular where, in the case of an action for annulment of a decision declaring aid compatible with the internal market, the applicant’s market position would be substantially affected by the aid to which the decision at issue, of which it is not the beneficiary, relates. It is therefore for the applicant to adduce pertinent reasons to show that the Commission’s decision may adversely affect its legitimate interests by substantially affecting its position on the market in question. As for determination that an adverse effect is substantial, the applicant undertaking cannot rely solely on its status as a competitor of the undertaking in receipt of aid but must additionally show that, having regard to the extent of its participation in the procedure and to the extent of the detriment to its market position, it is in a factual position which distinguishes it individually just as in the case of the person addressed.

Persons other than those to whom a decision is addressed may claim to be individually concerned by a decision within the meaning of the second paragraph of Article 263 TFEU only if that decision affects them by reason of certain attributes which are peculiar to them or by reason of circumstances in which they are differentiated from all other persons and by virtue of these factors distinguishes them individually just as in the case of the person addressed.

When the Commission adopts a decision under Article 4(3) of Council Regulation No 659/1999, laying down detailed rules for the application of Article 108 TFEU, finding that aid is compatible with the internal market, it refuses by implication to initiate the formal investigation procedure laid down in Article 108(2) TFEU and Article 6(1) of Regulation No 659/1999. The interested parties, which, in accordance with Article 1(h) of Regulation No 659/1999, are any persons, undertakings or associations whose interests might be affected by the granting of aid, in particular undertakings that are in competition with the recipients of that aid and who are intended to benefit from the procedural guarantees of the formal investigation procedure, may secure compliance therewith only if they are able to challenge the aforementioned decision before the European Union judicature. In those circumstances, their action can then only be one which is intended to safeguard the procedural rights available to them under Article 108(2) TFUE and Article 6(1) of Regulation No 659/1999. Consequently, where aid intended to support the deployment of next generation broadband networks in a specific region by a telecommunications operator is declared compatible with the internal market, the rival telecommunications operator in the market for the provision of specialist telecommunications services must be considered an interested party for the purposes of Article 108(2) TFEU, with standing to bring proceedings against the contested decision in so far as, by its action, it seeks to safeguard its procedural rights.

As for the pleas that may be raised by ain interested party, it is possible to take account of arguments on the substance only in so far as those arguments are capable of supporting a plea that doubts exist to justify the opening of the formal investigation procedure. However, the arguments must be defined in terms that are connected with the fact to be proved, namely the existence of doubts as to the compatibility of the measure in question with the internal market. In those circumstances, the EU judicature can therefore take into account pleas based on manifest error in assessing the facts and the existence of an abuse of a dominant position only to the extent that they are based on arguments intended to show that the Commission did not overcome doubts encountered during the preliminary investigation phase.

Moreover, the interested party bears the burden of proving the existence of doubts, and it may furnish such proof from a body of consistent evidence concerning (i) the circumstances and the duration of the preliminary investigation phase and (ii) the contents of the contested decision. Moreover, it is for that party to identify the evidence relating to the contents of the contested decision in order to prove the existence of doubts. In that regard, where the applicant simply refers to the arguments raised in respect of another plea, it must identify precisely which of the arguments raised in that respect are, in its view, capable of proving the existence of such doubts. In that context, if the applicant simply refers to the factual summary in the application and the arguments relating to the pleas, that vague and wholly unsubstantiated reference does not enable the Court to identify the precise factors raised in the context of the pleas which, in the applicant’s view, prove the existence of doubts and substantiate the pleas.

(see paras 42, 47, 69-71, 82, 88-90)