Almost a million fixed-rate mortgage customers may be losing out significantly by not carrying out a review of their arrangements, according to a report by Moneyexpert.

The firm showed that 970,000 people who signed up to fixed-rate deals at an average of 5.3 per cent in 2004 could be paying £948 a year more than they need to now that interest rates have lowered, and mortgage rates with them.

Moneyexpert chief executive Sean Gardner explained: "Homeowners need to keep their wits about them if they don’t want to end up paying over the odds for their mortgages. The price of doing nothing can be steep.

"Interest rates have moved since 2004 and the mortgage market is different from two years ago. What was a great deal then is not quite as good now. Savvy homeowners can stay ahead of the game if they do a bit of homework and review the market."

Those who do not move swiftly when their current fixed-rate deal expires run the risk of being tacked onto their lenders' standard variable rates (SVR) – which can measure up to six per cent.