Credit card interest is at an all-time high, yet two-thirds of borrowers don’t know how much they are paying and, as a result, have no idea what they could save by transferring their debt.

The Bank of England’s base lending rate has been at a record low of 0.5 per cent for seven years, but the average annual percentage rate charged on card purchases is a staggering 21.6 per cent, according to Moneyfacts.co.uk.

Unsurprisingly, while people are borrowing more than ever on plastic, almost half later regret these spending decisions and many are struggling to stay on top of the repayments.

TSB calculates that the typical British adult now has personal debt, excluding mortgages and student loans, of £3,598, with almost half owing the bulk of this on credit cards.

Forty-four per cent told the bank they suffer from “debt regret”. Despite this, 65 per cent don’t know their interest rate, meaning they can’t be sure how much they are being charged each month.

Many face being in debt for years to come. Financial watchdog the FCA says 1.6 million people repeatedly make just the minimum monthly repayment, and five million cards will take over 10 years to clear at the current rate.

Mike O’Connor, chief executive of debt charity StepChange, said: “People can be drawn into a false sense of security by low minimum repayments, but repeatedly making the minimum repayment on a credit card will turn what is meant to be a short-term product into a long term and costly one.”

StepChange says someone who owed £1,000 and made just the minimum repayment – around £24 a month – could take more than 18 years to clear their debt. Increasing this to £35 could reduce the term to just over three years and save almost £950 in interest.

For those with a good credit rating, the easiest way to free up cash for higher repayments is to switch to a cheaper card. Even moving a relatively modest debt could save hundreds of pounds and dramatically reduce the time it takes to repay.

According to Moneyfacts, someone spending £1,000 on a card charging 21.6 per cent and repaying £35 a month could be debt-free seven months earlier and save a further £276 in interest by switching to one with a rate of just 6.4 per cent.

Meanwhile, someone with a store card charging 29.9 per cent swapping to a 6.4 per cent alternative would pay just £86 interest, a saving of £510. Bank of Scotland, Lloyds, Halifax and Virgin Money all have cards with this low long-term rate.

Better still, if the same cardholder applied for one of those offering between 38 and 40 months interest free on balance transfers, provided they cleared the debt before the end of this, their only cost would be a transfer fee of around £28.

Those with a poor financial history won’t qualify for best-buy deals like these, but they may still be able to improve their situation.

Rachel Springall, Moneyfacts’ finance expert, said: “Not all borrowers will be offered the best rates, and some may not have the shiniest credit rating, which all leads to more expensive deals being turned to.

“For this reason, borrowers would be wise to get a credit check before applying for credit, so that they can get an idea of what their borrowing footprint looks like, and therefore, what kind of deal they are likely to secure.

“Borrowers should also be prepared to do the maths to work out what the true cost of their borrowing will be.”

Store cards tend to be among those charging the highest rates. Customers are tempted to take them out by the promise of discounts on initial purchases, but unless the debt is cleared right away, the interest charged soon outweighs the savings made.

Ms Springall said: “Getting on top of debts should be the top priority of any spender. Taking advantage of more cost-effective cards and spreading a debt on an interest-free deal means consumers can then concentrate on clearing it for good without huge amounts of interest adding to the bill.

“Those who move their debts to a better deal will clear a balance much faster than if they stayed put, and they will then be able to put aside some savings for spending in the future, which means they won’t have to rely on the plastic quite as much.”

Tesco Bank has a card offering up to 40 months interest free on transfers with a fee of 2.69 per cent. Halifax, Virgin, MBNA, Lloyds and Bank of Scotland all have options with an interest-free transfer period of 38 or 39 months and broadly similar fees.

All except MBNA also give between three and six months free on new purchases, and all have a long-term interest rate of 18.9 per cent.

Matt Sanders, credit card spokesperson for Gocompare.com, said: “The balance transfer battle that’s waged over the past few years is good news for customers looking to manage their existing balances over a longer period of time, as there are some exceptionally good deals available to those who shop around.

“However, those considering these cards need to remember that after the initial zero per cent period ends, they’ll be charged interest on the remainder of the balance, making it important to keep on top of when your deal expires.”

Anyone needing longer than these cards allow to clear what they owe would be wise to make a second transfer at the end of the interest-free period.

Those looking for longer to pay off new purchases can get between 25 and 27 months interest free with Post Office Money, Clydesdale or Sainsbury’s banks.

Cardholders struggling with existing borrowing should get help from an impartial expert before things deteriorate further. The Money Advice Service’s website, moneyadviceservice.org.uk, has clearly written sections on taking control of debt.

Other sources of free help include StepChange (stepchange.org or 0800 138 1111), the National Debtline (nationaldebtline.co.uk, mymoneysteps.org or 0808 808 4000) and the Debt Advice Foundation (debtadvicefoundation.org or 0800 043 4050).