After coming under fire for their blessing of risky mortgage-backed securities in the lead-up to the financial crisis, credit -rating agencies are again facing criticism, this time for misjudging the impact of the rebound in the US housing market.

Rising house prices in almost all US cities mean that many mortgage-backed securities once judged close to worthless may now be fit for an investment grade credit rating that would allow traditional investors such as pension or mutual funds to buy them. However, a growing number of investors who do not rely on such ratings said that the agencies, including Standard & Poor’s, Moody’s and Fitch Ratings, had not kept up with improving fundamentals.

“They’ve been so unimportant to our deployment of the marginal dollar in this market that they are irrelevant,” said Colin Teichholtz of Pine River, a hedge fund that manages $14bn of assets.