Shares in Natixis surged nearly an eighth this morning after the French bank's parent companies confirmed plans to inject $1.5bn (€1bn) into its financial guarantee insurance unit to stave off a credit rating downgrade that would have crippled the unit's ability to do business.

The move came barely a fortnight after Fitch Ratings warned in a research note on bond insurers that Natixis' wholly-owned CIFG unit is the "most likely to experience pressure in their capital cushions due to relatively high structured finance collateralised debt obligation exposure". The rating agency warned there was a high risk of a downgrade for CIFG.