A week later we had a product which fitted that category and we would have done much better. It’s a gross distortion and utterly unfair.”Which? says it looked at the best penalty-free variable rate deal offered by the big providers, so it could easily compare the costs. The best mortgage deal came from Shepshed building society in Loughborough, Leicestershire, with a rate of 4.25 per cent and a guarantee it will not go more than 0.50 per cent above Bank of England base rate.The magazine looked at current accounts, easy access savings accounts, mini-cash Isas, personal loans, credit cards, mortgages and insurance, and compared its own best buys in the market with the deals offered in the high street by the 11 biggest banks and building societies, excluding their internet offshoots such as Egg or Intelligent Finance. Together, these financial giants have 90 per cent of the banking market, so they have huge power and the ability to influence the financial decisions of millions of people.Helen Parker, the editor of Which?, says: “None of the banks can be relied on to give you consistently good value and, in some cases, they’re just plain expensive.

So next time you need a loan or a savings account, don’t just pick up the phone to your bank. If you shop around, there’s a good chance you’ll find a much better deal elsewhere, and the savings you make could add up to hundreds of pounds. And if you find yourself stuck in an uncompetitive account, switch. If you make the right choice you could be a lot better off.”It is not even possible to assume that any one banking group will be consistently best or worst.

Although Direct Line was the best buy among personal loans, its parent, Royal Bank, came bottom of the same table with an overall cost of £6,391 for £5,000. NatWest, another Royal Bank offshoot, rated only two places higher on £6,082. Which? points out that Royal Bank’s internet site charges only 9.9 per cent, which on the £5,000 loan used as the basis of its table, would work out £600 cheaper than the branch rate.David Outhwaite, a Royal Bank spokesman, said: “It all depends on the criteria they set, but the banks within our group have always been separate and competing with each other. Direct Line is phone and internet, and Royal Bank and NatWest are full-service banks with branch networks as well as phone and internet. In any case, our experience is that people choose an account on far more factors than interest rate alone.”The annual cost of borrowing on a credit card is just as variable, ranging from £22 from the US-owned Capital One Circle Rebate Mastercard to £52 for the Bank of Scotland Classic. Which? says: “Which card is best for you depends on how you use it. If you pay off the balance in full every month, the APR doesn’t matter, but if you tend to have a balance outstanding, a low interest rate of 13 per cent or less is more important.