France admitted on Tuesday its growth projection for 2012 was “probably too high” but pledged to take all necessary measures to preserve its triple-A sovereign debt rating, following a warning from Moody’s, the US credit rating agency, of a possible cut in its outlook to negative from stable.

The extra cost France has to pay over Germany to borrow rose to a 21-year high after the Moody’s note, with 10-year yields over Germany jumping to 103 basis points – the highest level since November 1990 – and the yield on its 10-year debt moved to 3.08 per cent.

Shares in French banks, which are heavily exposed to sovereign debt, fell sharply on the news. BNP Paribas was down 6.5 per cent in morning trading, with Société Générale off 6 per cent and Crédit Agricole down 5 per cent.