Uncertainty over the implications of Dodd-Frank Wall Street Reform and Protection Act, which was signed into law yesterday, has led Standard & Poor's, Moody's and Fitch to ask directly or imply that their ratings should no longer be used in any new debt issues.

In a statement issued by Fitch on Monday, it said it could not "consent to including Fitch credit ratings in prospectuses and registration statements at this time".

S&P and Moody's have each issued their own similar statements, as the agencies assess the impact of the new regulation which could expose them to more legal action in future from debt investors.

Royal Bank of Scotland analysts said the move by the agencies could make new issues of some bonds "difficult or impossible" as credit ratings are at the core of the marketing process and many investors require them before they can invest.