US consumers are defaulting on credit card payments at a significantly higher rate than last year, raising the prospect of problems in the stricken US subprime mortgage market spreading to other types of consumer debt.

Credit card companies were forced to write off 4.58 per cent of payments as uncollectable in the first half of 2007, almost 30 per cent higher year-on-year. Late payments also rose, and the quarterly payment rate - a measure of cardholders' willingness and ability to repay their debt - fell for the first time in more than four years.