It will come as part of a global review of banks to be announced when the US markets close tonight.
The Telegraph reports that the British banks affected could face downgrades of as much as two notches reflecting troubles in the eurozone.
Funding costs will inevitably rise for these lenders as their perceived risk rises.
Santander UK, the Spanish owned bank, has already seen its rating downgraded by Moody’s as have various other Spanish and Italian banks.
Tony Ward, chief executive of Home Funding, said the downgrades wouldn't necessarily cause mortgage rates to rise however.
He said: "If funding costs rise and there are write downs against Tier I capital then they will be under pressure but it is worth remembering that mortgage lending for each of these lenders is a core product/strategy and that under the Internal Ratings Basis of capital allocation are relatively low capital consumptive products.
"So you could put a case together to say that mortgages will be affected less than some other asset classes. Not good news overall of course but maybe not the end of the world for mortgage lending."
