The study by scientists at a British medical charity found that the creams fail to stop harmful rays of the sun from penetrating the skin.

Professor Roy Sanders, a consultant plastic surgeon with RAFT, the Restoration of Appearance and Function Trust, said suncreams were much less effective at blocking ultraviolet A (UVA) light, which can cause the skin cancer melanoma, than UVB.

"When ultraviolet A impinges on the skin it triggers the release of highly reactive chemicals called free radicals which we believe can induce a malignant change," he told BBC Radio.

"Since ambient sunlight is principally ultraviolet A and since sunscreens protect mostly against ultraviolet B, if we use the sunscreens it may increase the risk of us developing a rather unpleasant cancer called malignant melanoma," he said.

On the rise

Cases of malignant melanoma have doubled every 10 years since the 1950s and the cancer now kills about 1500 people in Britain every year.

RAFT, which published the research on its website on Monday, predicts that by the year 2010, the lifetime risk of the disease will approach one in 50 of the British population.

Sanders and colleagues at RAFT exposed skin samples removed from consenting patients during surgery to UVA light at intensities similar to that of sunlight.

"We're lulled into a sense of false security ... and so people are inclined to take a much greater dose of the sun"

Professor Roy Sanders, 
Cconsultant plastic surgeon

The skin had been treated with three popular high factor suncreams which say they contain some UVA protection. While the creams prevented the sun from burning the skin, they did not stop UVA rays from penetrating it, RAFT said.

Sanders said the concern was that people were using the creams believing that they offered protection against cancer and, comforted by that, might be putting themselves at risk.

"We're lulled into a sense of false security ... and so people are inclined to take a much greater dose of the sun," he said.

Wear a hat

But he cautioned people not to abandon suncreams, which protect against two other malignant skin tumours, and said they should also wear hats and t-shirts and stay in the shade.

Health and beauty retailer Boots, a leading manufacturer of suncreams in Britain, welcomed RAFT's research, but said it was unrealistic to ask people to stay out of the sun.

"We've already reformulated our products for next year to include even higher UVA protection," the retailer said in a statement.

"At the moment, using a good sunscreen and being sensible is still the best way to stay safe in the sun."