By Olivia Bugault

Santander UK--fully owned by Banco Santander SA--said Tuesday that aftertax profit fell in its first half and booked higher credit impairment losses

The bank said after-tax profit during the period fell to 128 million pounds ($167.3 million), compared with GBP410 million the year prior.

Net interest income for the first six months of the year fell to GBP1.55 billion from GBP1.67 billion, while it booked GBP376 million in credit impairment losses, it said.

Credit impairment losses included "GBP267 million arising from changes to economic scenarios and weights, the staging reclassification under IFRS 9 of certain loans following an in-depth sectoral review and the treatment of payment holidays," it said.

Write to Olivia Bugault at olivia.bugault@wsj.com