Credit cards are offering the longest ever zero per cent promotional deals on balance transfers and purchases, but average interest rates are continuing to rise.

Despite the base rate remaining unchanged for more than a year, credit card providers have not let that stop them from increasing their interest rates, according to analysis from moneysupermarket.com.

Consumers might be enjoying the longest ever introductory special offer periods on interest-free balance transfers and purchases, but they are paying the price when these interest-free periods come to an end.

The average purchase interest rate on the top credit cards has crept up to 17.32 per cent, the comparison website has found, from 17.19 per cent in May.

The average zero per cent balance transfer credit card period on the top best buys is 15.4 months, nearly three months longer than it was in July 2007, with some offering as much as 16 months.

Those consumers looking to make interest-free purchases on their credit card will find they offer average promotional periods of 12.2 months, compared to 10.8 months in July 2007.

Commenting, Kevin Mountford, head of banking at moneysupermarket.com, said: “An interest-free balance transfer card or purchase card can be a great option for people with existing debt who need flexibility, or for those who have a big purchase coming up and need some extra time to pay it off.

But, he warned consumers that rising average interest rates when these deals end are the “sting in the tail” of longer promotional periods.

“This makes it even more important to ensure you pay your balance off before the interest-free period ends,” he urged. “You also need to make sure you aren’t late making a repayment. If you are, or if you miss one completely, not only will you be hit with a late fee, you’ll probably forfeit the zero per cent offer and start being charged interest.”

© Fair Investment Company Ltd