Savers are losing £3.5bn a year in interest due to switching inertia.
Many people are loyal to high street banks, but these often offer worse rates than smaller, rival firms.
Customers with Barclays, HSBC, Lloyds, Royal Bank of Scotland and Santander have £827bn of the total £1.3 trillion saved in the UK, according to the Centre for Economics and Business Research, a consultancy.
The study, commissioned by savings platform Flagstone, found that these customers would make £3.4bn in interest on their savings over the next year. But this would more than double, to £7bn, if these savers swapped to better deals with rivals.
Santander has the highest interest rate for any instant saver account from the high street banks listed, at 0.4pc. But Virgin Money pays 1.5pc for a similar deal.
The same is true in many other savings areas. All the current top rates for one- to five-year bonds and Isas are for deals supplied by non-high street lenders.
A YouGov survey found that more than four in 10 savers would be tempted to switch accounts if savings deals were more generous and paid an extra one percentage point in interest.
Almost a quarter (24pc) of the 4,207 people surveyed said banks would need to offer them an extra two percentage points to move.
Andrew Thatcher, of Flagstone, said: “This study reveals the high-levels of inertia in the cash deposit market and the challenges that non-high street banks face in raising deposits.”
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