Savers are missing out on up to £12 billion in interest by holding their money in accounts paying low returns, a consumer group has said.
Which? said half of the 1,200-plus savings accounts available in the UK paid interest of 0.5% or less, while a quarter pay just 0.1% or lower.
It said if all savers moved their money to an account paying one of the highest rates available consumers would collectively receive an extra £12 billion a year, or £322 each.
The group said few banks made it clear how much interest customers were being paid on their statements, while they also failed to alert people to the availability of better rates.
Peter Vicary-Smith, chief executive of Which?, said: "Banks are depriving British savers of £12 billion a year by keeping us in the dark about the pitiful interest paid on hundreds of savings accounts.
"Whilst we pressure the banks to be more upfront about their rates, people can take action and potentially add hundreds of pounds a year to their savings by moving their money to a better account."
But the British Bankers' Association said it was easy for savers to find out what returns they were receiving on their cash, while banks would notify them about any significant changes.
It said: "Information is readily available in branches, online and from a variety of other sources, including newspaper best-buy tables and comparison websites and customers will also be automatically notified if there are changes resulting in materially lower rates so they can switch their funds.
"Savings rates vary depending on the amount customers have to save and the time they can afford to leave the cash untouched.
"As with any product or service, it always pays to shop around for the deal which is best for you."