Nearly half of all consumers with a 0per cent credit card have been hit with high interest rates when their introductory deal has ended.

Almost a third said they had not received any notice that the 0per cent period was over, and credit card holders have incurred an average £267 in charges, according to comparison site uSwitch.

It wants the Financial Conduct Authority, which is about to publish a final report on the market, to do more to stop banks encouraging borrowers to take on more debt.

Tashema Jackson at uSwitch.com, says: “Credit card providers are wooing consumers with tempting 0per cent deals but when the rates rocket without warning, the honeymoon period is definitely over. We are calling on providers to give customers clearer and more prominent notice before jacking up the interest rate, to help people better manage their debt.”

The industry’s Lending Code requires lenders to inform customers four to eight weeks before the introductory offer ends “on the front of the statement or in a separate, prominent personal notification to the customer”. Of those surveyed, 85per cent said that if they had seen a prominent warning that their deal was due to expire, they would have considered switching to a better deal.

Even when borrowers do try to plan, they are unclear when the interest-free period actually starts.

For most providers, the clock starts ticking as soon as a borrower is accepted for a card. But 16per cent of borrowers think it begins when the card lands on their doormat and 20per cent believe it’s only when they transfer their first balance.

It comes as borrowing on credit cards, overdrafts and loans is racing ahead at 14 times the rate of just two years ago -

personal debt jumped by 5.8per cent in the year to March, to £87billion. In March 2014 the annual rise was just 0.4per cent.

Two years ago RBS broke ranks with the big lenders by committing itself to “no teaser rates” on credit cards.

At the time the bank said: “The credit cards industry is absolutely dominated by teaser rates, trapping people into a spiral of debt that they never pay down.”

RBS said market data showed that two thirds of customers who use 0 per cent balance transfers do not pay back their debts before hitting the deadline when the teaser rate ends, and an average customer owing £9000 on credit cards and transferring to a new one would then continue to increase borrowings.

The bank replaced its 0 per cent balance transfer cards with a card that charges a flat 6.9 per cent interest – but there is also a £2 a month fee.

Interest-free periods on cards, which a decade ago were never more than 12 months, have now reached 40 months, with the latest card from Sainsburys Bank carrying a 2.89per cent balance transfer fee, while Virgin Money’s fee is 2.59per cent and MBNA charges only 2.55per cent. There are 39-month cards from Halifax (2.48per cent) Tesco Bank (2.69per cent) and Bank of Scotland/Lloyds Bank (2.95per cent), according to Moneyfacts.co.uk.

There is currently £60bn outstanding on credit cards with a massive £25bn interest free (from 0per cent purchase and balance transfer promotions).

“The numbers are staggering,” says Andrew Hagger at Moneycomms. “The concern is that nobody really knows how much of this £25bn interest-free balance is being managed by people being smart with their finances compared with those struggling to make ends meet and simply using it as a means to keep their heads above water.

Mr Hagger says: “You have to question why lenders continue to offer long term interest-free credit but they no doubt factor in that a certain percentage of borrowers will miss a payment or exceed their credit limit – thus falling off the 0per cent wagon and straight on to a rate of 18.9per cent APR or more.”

A report last month by Debt Advisory Centre, a debt management company, found a quarter of women in Glasgow were relying on credit cards to pay for living costs such as rent, food and heating, and 10 per cent drew on it for cash when money ran low.