Strains among borrowers with patchy credit are rising, with more falling behind on their mortgages and fewer able to refinance their higher interest rate loans, according to a report by Standard & Poor's, the credit rating agency.

The report into the peformance of securities backed by so-called nonconforming mortgages shows that the total delinquency rate for mortgages rose to a record 23.31 per cent of the total pool as at June 30 - up from 22.17 at the end of the first quarter.