Fitch Ratings on Jan. 3 upgraded Santander UK PLC's long-term issuer default and senior unsecured debt ratings to A+ from A and removed the ratings from Rating Watch Positive.

The outlook on the bank's long-term issuer default rating is stable. The rating agency also upgraded the bank's derivative counterparty rating to A+(dcr) from A(dcr) and removed the rating from Rating Watch Positive.

At the same time, the rating agency affirmed the British bank's short-term issuer default and senior unsecured debt ratings at F1.

The upgrades follow an increase in the bank's subordinated debt buffer and reflect the Jan. 1 amended ratings of some £8.5 billion senior loans offered by parent company Santander UK Group Holdings PLC to make the loans eligible for the minimum requirement for own funds and eligible liabilities, according to Fitch.

Spain's Banco Santander SA is the ultimate parent of Santander UK.