Bradford & Bingley has warned people that "buy now - pay later" shop finance deals can leave them out of pocket.
The bank has said that if shoppers forget to stump up the cash before the interest-free period ends, or simply cannot afford to pay for the goods, they could end up paying double.
Michael Senior, head of personal lending for Bradford & Bingley, warns: "Generally, in-store payment schemes invite you to pay the balance in full at the end of the interest-free period.
"If you can't, then the balance - plus interest - has to be paid over a set period of time, typically by monthly direct debit, for anything up to five years.
"This can end up costing the consumer hundreds, even thousands, of pounds in interest, leaving the so-called 'bargains' being paid off long after even next year's sales have ended."
Bradford & Bingley gives the example of an armchair costing £799 from a leather sofa shop. The "buy now - pay later" deal offered with it promotes no deposit and nothing to pay for 12 months and, if you can pay in full after the interest-free period, you will incur no interest charges.
But if payment is not received in time shoppers are required to make monthly payments of £41.99 over 36 months seeing the total cost of the armchair would almost double to £1511.64.
"Sale buying can seem like a good idea but consumers need to be careful not to burden themselves with debts that take years to pay back. If you don't shop around for the best payment option then your 'bargains' in January could take you up to five years to pay back and end up costing you hundreds, even thousands, of pounds more," said Mr Senior.
Bradford & Bingley points out that using a personal loan to fund the purchase could well work out cheaper. Another option is making the purchase on a credit card which offers a zero per cent interest on initial purchases.To compare prices for personal loans, click here.
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