The governor of France’s central bank attacked credit rating agencies yesterday, calling them “incomprehensible and irrational” as Paris braces for a potential downgrade of the country’s triple A status.

Christian Noyer, head of the Bank of France, said a French downgrade would not be justified on economic fundamentals. On that basis, he added, the agencies should begin by downgrading the triple A rating of Britain, which “has bigger deficits, more debt, higher inflation, less growth than us and where credit is shrinking”.

“We have put in place credible plans for dealing with our deficit – the credibility of our plan can be seen in what happened with the interest rates on our bonds,” said a spokesman for David Cameron, UK prime minister. “The markets clearly don’t agree with Noyer,” added a UK Treasury official. Privately British officials were astonished by the remarks.