Gas companies have been raising prices

In the advert a British Gas customer, animated as a flame, said he would not change provider because all energy suppliers were raising prices.

The ASA said this wrongly implied that people would not benefit by switching.

British Gas said the ASA's decision was "harsh" and that switching suppliers would not mean avoiding price rises.

Factual claim

Four viewers and one competitor firm, Scottish Power, complained to the ASA about the adverts, which ran last November.

This advert gives a genuine customer's opinion. It's not scripted by a marketing man British Gas spokeswoman

The ASA investigated and said it considered the customer's testimonial to be a factual claim that British Gas users were unlikely to be better off if they switched suppliers.

It added that the evidence was that customers could in fact benefit from switching, therefore the advert was misleading.

British Gas justified the advert on the grounds that it was designed to show that all suppliers had put up their prices and it was difficult to compare costs.

"This advert gives a genuine customer's opinion. It's not scripted by a marketing man," a British Gas spokeswoman told BBC News.

"Our customers understand that energy price rises are a moving feast and switching supplier to save money when more rises may be imminent could be a false economy," she added.