INTM489896 - Diverted Profits Tax: notification, charging and payment: accounting period
For companies within the charge to UK corporation tax, “accounting period” means an accounting period of the company for the purposes of corporation tax.
A non-resident UK company which is not within the charge to UK corporation tax is assumed to have such accounting periods for the purposes of corporation tax as it would have had if it had carried on a trade in the UK through a UK permanent establishment by reason of the activities of an avoided PE.