Abbey found that the average overpayment made by customers with its Flexible Plus mortgage in any given month is almost £500, reaching a peak of £560 in November and dropping sharply to £215 in December. Even if this average payment of £500 were spread over the period of a year, it would save £11,300 in interest and pay off the mortgage one year and nine months early.

The average amount held in the savings offset facility is £22,000, which, if left untouched, would save £45,000 in interest and pay a mortgage off 5 years early.

Lal Tawney, Abbey’s head of mortgage marketing, said: “Our offset customers benefit in many ways. Not only will they pay a competitive rate of interest for the life of the mortgage without having to switch to a new deal, but any overpayments will reduce the interest charged as well as cutting the mortgage term.”

The Flexible Plus mortgage is available to both new and existing customers. It tracks the Bank of England Base Rate for the life of the mortgage.

Lal Tawney adds: “Some borrowers view remortgaging as a burden and they are not inclined to scour the market for the best deals. We recently found that over a third of people on a mortgage deal don’t intend to remortgage to a new rate and that many others don’t know what deal they are on or when it expires. With the Flexible Plus mortgage, borrowers can have the piece of mind that they are paying a competitive rate, and that it will last until they pay their mortgage off.”