Cooperative Bank said the number of customers making overpayments has increased by 50% in the last year.
This additional equity has helped cushion owners of family homes against house price falls and put them in a strong position to move on up the ladder when the market firms up.
PropertyIndex said that those with properties in popular locations, close to sought-after schools and with good transport links, would find it easiest to sell, but the equity cushion meant some sellers were able to afford to accept a lower price than expected for their own, to move on to a larger property which in many cases had dropped in price considerably more.
PropertyIndex Chief Executive Lee Bramzell said: "Thousands of middle-class homeowners have prudently compensated for the falling market value of their own home by overpaying on their mortgage and therefore maintaining their level of equity.
"We are now seeing evidence that buyers are deadly serious about re-entering the market, with a 40% increase in visitor numbers since March this year.
"Owners of three and four-bedroom family homes in desirable locations, particularly those close to good schools and transport links, will be well positioned to make a considerable jump up the ladder as the market stabilises.
"Not only have they maintained their equity but they will also benefit from price falls on the larger property they are buying, making them unexpectedly within their price range."
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