The BBC's Rory Cellan-Jones reports: "Banks were more expensive for a whole range of products"

Research by the association's Which? magazine found that banks offered poor value products that leave their customers out of pocket, it said.

Customers could save hundreds, or even thousands, of pounds by looking elsewhere for financial services, Which? said.

The report looked at 11 products, including mortgages, personal loans, insurance and credit cards, offered by the eight largest current account providers.

'Shop around'

Which? editor Helen Parker said: "Our research proves that most big banks offer appalling value for money.

"They reward customers' loyalty by selling them products that, in some cases, are nothing short of a rip-off.

"This is a case where shopping around is well worth the effort - it could literally save you thousands of pounds."

The bank's whose products were tested were Abbey National, Barclays, First Direct, HSBC, Lloyds/TSB, Nationwide Building Society, NatWest and the Royal Bank of Scotland.

Barclays' products were the poorest value, Which? said, singling them out for "consistent mediocrity".

Nationwide offered better value than the others, the report said, while Abbey National's savings accounts were praised.

NatWest had reasonably competitive home insurance and a good five-year mortgage, but its credit cards, savings accounts and personal loans were described as "appalling value".

Best deal

The survey found the best five-year fixed-rate mortgage on a £60,000 loan would cost £16,750 over the five-year term if home-buyers looked for the best deal.

None of the biggest eight matched the figure.

NatWest came closest with a cost of £17,396 over the five years.

The worst deal came from First Direct at £18,865, with Barclays at £18,843.