That’s almost doubled in a year from an equivalent £7.4bn last October, according to investment platform Hargreaves Lansdown.

More than a quarter (27%) of people have never switched savings accounts for a better rate and almost half (49%) have no plans to switch at any point, the firm said.

Its research showed that the most common reason for not switching was because people think they have the best rate already (28%), followed by the fact they trust their bank (27%) and then the hassle involved in switching (17%).

A year ago a third of people said they did not switch because rates were too low to bother with. That figure has now fallen to 17% as rates have risen so much in the meantime.

Last October, the best easy access savings accounts were paying less than 3%, whereas now they’re paying more than 5%.

Sarah Coles, head of personal finance at Hargreaves Lansdown, said: “Sticking with easy access branch accounts run by the high street giants paying miserable levels of interest is costing savers a fortune.”

The research suggested the biggest motivation for people to stay put is because they think they already have the best possible rate (28%).

Ms Coles said: “This may be the case for some, but given that the lion’s share of money is still in the easy access accounts of the big high street giants, and the vast majority of them pay a fraction of what’s available from newer online banks, there’s a reasonable chance others just don’t realise how much more rates have risen elsewhere.”

The second most common reason for money languishing in miserable accounts is that people trust their bank (27%). But given that newer banks usually offer the best rates, savers need to consider how much interest they’re losing by choosing not to trust a bank on the grounds it doesn’t feel as familiar, said Ms Coles.

• Calculations are based on earning 5.15% in an easy access account. Savings data from the Bank of England’s most recent figures (September) and switching data from a survey of 2,000 people by Opinium for Hargreaves Lansdown in October 2023.