Are you planning on switching your credit card balance to a new piece of plastic in the new year? With such a huge range of cards charging 0 per cent on balance transfers, you could help to offset the cost of your Christmas shopping with big savings on the interest charged.

However, increasing numbers of borrowers are falling foul of the small print in credit card contracts, which forbids them from transferring balances to a card that is owned by their current card provider.

This is a serious stumbling block for consumers because only four companies operate 70 per cent of credit cards, says Moneysupermarket.com, the financial website.

Card companies say that 0 per cent balance-transfer deals are designed to entice new customers and that it does not make business sense to allow an “existing” customer to avoid paying interest by switching between cards from the same group.

For example, someone who tries to transfer the balance from a NatWest card to a Mint card will be turned down because both cards are owned by Royal Bank of Scotland (RBS). Likewise, a borrower who wants to switch the balance from Virgin to Alliance & Leicester will also be frustrated because both cards are operated by MBNA.

Rob Kenley, head of credit cards at Moneysupermarket, says: “This is a common issue now because the main providers have so many more credit cards in their stables. Even though two cards look different and are branded uniquely, they may well be issued by the same provider. People with outstanding balances need to be aware of this, because you cannot swap oranges with oranges, only with apples or lemons.”

There are 400 different credit cards available in the UK. But MBNA alone issues 189 of these. Among the other main players, HBOS issues 51, but it does allow balance transfers between five of them, including the AA and Sainsbury’s Bank cards. The Cooperative Bank and Lloyds TSB issue a further 41 cards between them. The best-buy table for 0 per cent balance-transfer deals is dominated by MBNA and RBS, who each have four cards in the top ten.

Laura Mottram, of RBS, says: “I am afraid that these deals are promotional offers designed for new customers. It is not worth our while to allow customers to remain on a 0 per cent deal indefinitely.”

Paul Lawler, of MBNA, says that transfers between its cards are refused because the amount that you owe does not change. MBNA says that it would happily accept applications from existing customers, but it would then prevent them from transferring balances. It says that these restrictions are explained in the terms and conditions.

Borrowers who try unsuccessfully to switch a balance will then be stuck with an unwanted card and an available credit limit of thousands of pounds, which they do not need.

Mr Kenley says that an additional problem is that an application for a new card will produce a footprint on your credit report, which could affect your credit rating. He says: “Because providers now share information about the amount of credit available to you, that can count against you when applying for another card.”

Experts say that a borrower who is planning to apply for a card should first find out about the parent company of both the existing card and the new card. But for those who pick carefully, there are some eye-catching deals available. In pole position is the Virgin Credit Card, which charges no interest on balance transfers for the first 15 months, although there is a fee of 2.98 per cent.

The credit cards from Sony, Cheshire Building Society and Alliance & Leicester – all operated by MBNA – charge no interest on balance transfers for a year, with a slightly higher fee of 3 per cent. The interest charged on purchases is 15.9 per cent.

What’s in your wallet?

MBNA (MBNA card)

Operates cards for

Alliance & Leicester

Cheshire Building Society

Sonycard

Virgin credit card

HBOS (Halifax card)

Operates cards for

Cancer Research UK

Amazon.co.uk

Intelligent Finance

NSPCC charity card

Royal Bank of Scotland (RBS card)

Operates cards for

NatWest

Mint

Tesco

Ulster Bank (NI)

The CoOperative Bank

Operates cards for

Northern Rock

Smile

Stroud & Swindon Building Society

Yorkshire Building Society

CASE STUDY: 'A weight off my mind'

Wesley Price, of Stockport, has moved £680 from his Egg credit card to a new Barclaycard with 0 per cent interest on balance transfers for 12 months. He checked that he would be able to move his balance before applying.

Mr Price, 25, took out the Egg card when he was at university because purchases were interest-free for six months. When he transferred his balance last month the rate had climbed to 21.9 per cent.

He says: “I had to pay a 2.5 per cent balance transfer fee but it was a weight off my mind. The Egg interest rate was too high for me to manage.”