1. Where institutions have received the prior permission of the competent authorities, institutions permitted to use the IRB Approach in the calculation of risk-weighted exposure amounts and expected loss amounts for one or more exposure classes may apply the Standardised Approach for the following exposures:
(a) the exposure class laid down in Article 147(2)(a), where the number of material counterparties is limited and it would be unduly burdensome for the institution to implement a rating system for these counterparties;
(b) the exposure class laid down in Article 147(2)(b), where the number of material counterparties is limited and it would be unduly burdensome for the institution to implement a rating system for these counterparties;
(c) exposures in non-significant business units as well as exposure classes or types of exposures that are immaterial in terms of size and perceived risk profile;
(d) exposures to central governments and central banks of the Member States and their re
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