Fears US regulators will rule that thousands of Americans may have been unfairly evicted from their homes rattled Wall Street today as the scandal over the use of "robo-signers" escalated.

Employees at mortgage firms are alleged to have rubber-stamped documents to force out defaulting homeowners without following the correct procedures.

Shares in Bank of America, Citigroup, Wells Fargo and JP Morgan all fell sharply after it emerged that Xee Moua, an employee at Wells Fargo, the second-largest US mortgage servicer, had pushed through 500 foreclosures a day.

The growing scandal over the way homeowners have been evicted came as property data firm RealtyTrac reported that the number of houses seized by banks topped 100,000 for the first time in September. Lenders took possession of 102,134 properties in September. The state with the highest rate was Nevada.