The expected move is part of the rating agency’s wider downgrade of major world banks amid the deepening eurozone crisis, reports Sky News.
Confirmation of the downgrades, which could potentially add billions of pounds to the funding costs of impacted institutions, is expected after US markets close this evening.
Barclays, HSBC and state-owned lender RBS are reportedly among the banks under scrutiny as the global financial crisis piles more pressure on lenders.
Banks across the Channel, including Societe Generale and BNP Paribas, could also be hit by the action, in addition to Wall Street giant Goldman Sachs and Morgan Stanley.
Sky added the move, which may affect up to 18 lenders, is part of a wider reassessment of the health of the global banking industry by the agency.