The war isn’t over! Seven years ago, when 0 per cent credit-card deals were in their infancy, I first revealed my practical guide to what is now called stoozing: making a profit from credit cards.

Gradually plastic providers hit back, and many believe the death knell was sounded by the recent widespread introduction of fees for transferring debts to 0 per cent cards. But they’re wrong. The only thing that has changed are the tactics. You can still make up to £1,200 a year from your card firm – completely free.

The essence is simple: if credit card companies will lend money at 0 per cent, you can borrow it and then save it at a high interest rate so you’re earning money on cash they have lent you for free. My fondest stoozing memory is being lent thousands of pounds on Egg’s credit card only to shove it into Egg’s savings account, so it paid me hundreds of pounds in interest on its own money.

The largest stooze I’ve heard of was £80,000 of debt put into an offset mortgage, netting that stoozer nearly £5,000 a year in reduced interest payments.

Only those free of overdrafts, credit cards or loans should attempt this; otherwise reducing interest on debts is a better bet.

Stoozing for beginners

Card providers have introduced balance-transfer fees when debts are shifted to interest-free offers, but cards offering 0 per cent on purchases escape the fees, making them the core equipment for building your “stooze-pot”.

The longest 0 per cent deal on purchases is from HSBC at 12 months, but only for applications in branches or over the phone. It is followed by 10 months at 0 per cent on Sainsbury’s Visa, Barclaycard Platinum and the Sky card. With the latter you also get reward points off Sky products. While the &More card from Marks & Spencer charges no interest for only nine months, it rewards an extra £5 to spend instore for every £1,000 spent.

Use the card to replace all credit card, debit card and cash spending.Don’t pay off this debt; instead set up a direct debit to make the minimum monthly repayments. Because you are spending on the card, money isn’t being withdrawn from your current account, which means cash is building up. You can then move this into a savings account.

What to do with the cash

Keep the money in a risk-free easy-access account, such as a tax-free cash Isa, which can shelter up to £3,000 a year. If you have used up your allowance, put the cash in a high-paying instant-access savings account.

How to boost the gain

At this point your 0 per cent card debt should be matched by savings earning you roughly 6 per cent. When the 0 per cent period is coming to an end pay off the debt with the savings. If you had £20,000 of credit-card debts at 0 per cent and put your cash in an account at 6 per cent, you would earn £1,200 in a year.

Alternatively, at the end of the 0 per cent period, shift the debt to a new card with a long interest-free balance-transfer offer and keep earning. This usually means paying a balance-transfer fee of about 2 per cent of the debt shifted, but it is still profitable.

For example, if you have £6,000 stoozed you could shift it to the Morgan Stanley Buy & Fly card, which charges 0 per cent for nine months with a fee capped at £50; yet you could earn £225 interest over this period.

Advanced stoozing

There is a more advanced technique that gives you access to all the 0 per cent cash immediately, allowing you to quickly build a bigger sum and boost profits. Yet it is complex and easy to mess up, so it is only for moneysaving nerds. For a fuller explanation, go to moneysavingexpert.com/stooze .

Get an Egg Money card (not the normal Egg card), the hybrid credit card and current account which allows both a positive balance on the card and the ability to pay money directly into bank accounts without a charge.

Then get a credit card with a fee-free 0 per cent offer for balance transfers. At the moment the longest are six months from Stroud & Swindon and Norwich and Peter-borough building societies.

To start with you have an Egg Money card with a zero balance and a 0 per cent balance-transfer card with nothing on it. The first step is to ask your 0 per cent card provider to transfer a £3,000 balance from Egg Money. In practical terms this means it will pay £3,000 off the Egg Money card, even though no debt exists there.

This shouldn’t be a problem, as most credit card terms don’t specify a debt must exist to do a balance transfer, but if asked don’t lie, as that would be fraud.

Now your Egg Money card is £3,000 in credit and you have £3,000 in debt on your balance-transfer card. You then put the money into your high-interest savings account. Use Egg Money’s facility to switch cash to your current account, then to a savings account in the normal way.

The impact of stoozing on credit scores

Most lenders’ scoring systems aren’t sophisticated enough to detect stoozing. Yet multiple applications and high outstanding debts diminish your ability to get competitive credit, so spread out card applications. And don’t stooze if you need your credit score for real borrowing.

Martin Lewis is the creator of Moneysavingexpert.com, a free website dedicated to showing people how to save money