An institution that is permitted to apply the IRB Approach in accordance with Article 107(1) shall, together with any parent undertaking and its subsidiaries, implement the IRB Approach for at least one of the exposure classes referred to in Article 147(2), point (a), point (aa)(i) or (ii), point (b), point (c)(i), (ii) or (iii), point (d)(i), (ii), (iii) or (iv), or point (g). Once an institution has implemented the IRB Approach for a certain type of exposures within an exposure class, it shall do so for all exposures within that exposure class, unless it has received the permission of the competent authority to use the Standardised Approach permanently in accordance with Article 150.

Competent authorities shall determine the period over which an institution and any parent undertaking and its subsidiaries shall be required to implement the IRB Approach for all exposures within a certain exposure class across different types of exposures within the same business unit and across different business units in the same group, or for the use of own estimates of LGD or for the use of IRB-CCF. That period shall be one that competent authorities consider to be appropriate on the basis of the nature and scale of the activities of the institution concerned, or of any parent undertaking and its subsidiaries, and the number and nature of rating systems to be implemented.

Institutions shall carry out implementation of the IRB Approach in accordance with conditions determined by the competent authorities. The competent authority shall design those conditions in a way that they ensure that the flexibility under paragraph 1 is not used selectively for the purpose of achieving reduced own funds requirements in respect of those types of exposures or business units that are yet to be included in the IRB Approach or in the use of own estimates of LGD or in the use of IRB-CCF.