Up to 18 banks could see senior debt ratings cut several notches under the review, the ratings agency said, echoing similar moves in Portugal and Spain.

“The reassessment is not driven by either a deterioration in the financial strength of the banking system or that of the government,” Moody’s said.

UK authorities have made it clear that they will not always automatically step in if a bank fails, Moody’s said, leading the agency to reassess banks whose failure would not fatally hurt the whole financial system.

The bigger banks, including those bailed out by the UK taxpayer in the financial crisis such as Lloyds and Royal Bank of Scotland, will be scrutinized later and may until then be subject to negative outlooks.

On Wednesday, Moody’s cut seven Portuguese banks one or more notches, a day after downgrading Portugal’s creditworthiness, citing the probability the government could limit future support for lenders.

In Spain, 30 banks were cut in March after the sovereign had its own rating cut and Moody’s reassessed the “extraordinary levels” of systemic support many had benefited from until then.

The UK banks more immediately vulnerable to a downgrade are smaller institutions, including many building societies, rather than larger banks, including those still heavily supported by the state, Moody’s said.

It said it was reviewing the implicit government support incorporated into the senior debt ratings of these banks as they were unlikely to be deemed systemic in the medium term.

British banks benefited from up to five notches of uplift to their senior debt ratings during the crisis from implicit systemic support, Moody’s said.

Moody’s in March kicked off a review of systemic support for smaller financial institutions across Europe, on a country by country basis.