Treasury prices rose on Monday as fixed income investors sought a safe haven amid fears that repayment problems involving “subprime” US mortgage borrowers could have knock-on effects in the broader $8,000bn mortgage market and beyond.

The latest concerns centre on the Alt-A market, in which consumers with slightly better credit than the weakest subprime borrowers can obtain loans with loose terms - such as no proof of income. Late payments and defaults on such loans are running at four times the historical rate.