Article 21b(2) CRD states that competent authorities may allow institutions to have two intermediate EU parent undertaking, if certain requirements are fulfilled. 

We understand it as a formulation meant to generically point - as happens in other CRD provisions - at the prudential supervisors. Further, we understand that cases of joint decisions by the college of supervisors according to Article 116 of the CRD are explicitly spelled out (which does not apply in this example), if intended.   

Hence, the question arises, as to which competent authority should be considered competent for the decision when more competent authorities are involved in the supervision of subsidiaries in scope of the IPU requirement (e.g. two institutions subsidiaries of a foreign parent entity and each under the supervision of a different authority). 

In our reading the competent authority responsible for the approval to have two IPUs would be identified in analogy with Article 111 CRD (see "answer proposed by the submitter" below). The analogy with Article 111 CRD would point specifically to paras (3) and (5), as if all existing institutions authorised in the Union were part of a group subject to consolidated supervision having the same parent EU financial holding company. This is also proposed in the draft EBA GLs on the slightly different, yet connected, point of the authority in charge for receiving the forward-looking assessment and coordinating with other authorities. By contrast, Article 111(1) would be difficult to apply in practice and create arbitrage opportunities for firms, as the competence would depend on the size and location of an hypothetical credit institution (on top of the existing entities) that does not yet exist.