The research firm said rising employment levels disguise the increasing number of people in part time work.
It said while the base rate and mortgage rates remain low "it is possible that these forced part-time workers initially managed to keep up repayments. But for some at least, their finances may now have reached a tipping point".
Matthew Pointon, property economist at Capital Economics, said: "Although it is impossible to be sure, the trend towards ever greater numbers of people working parttime out of necessity rather than choice may have halted the downward trend in mortgage arrears.
"At the very least, however, this trend towards under-employment suggests that mortgage arrears may be unusually vulnerable to any future increases in mortgage payments."
Figures released earlier this week show unemployment fell by 46,000 to 2.56 million in the three months to June while the number of part-time workers rose by 71,000 to just over eight million, the highest since records began in 1992.
But Pointon added: "If unemployment rises as we expect, we think that mortgage arrears will follow. But without a much weaker economy than we expect, or a renewed crisis in mortgage funding markets, low mortgage rates will continue to help keep arrears low by the standards of past recessions."
