Until recently, those wanting to sport a winter tan without the expense of a long-haul holiday had to book a session under a sun bed or brave the beautician's spray gun.

However, according to a warning issued by regulators, the search for a sun-kissed body has recently taken a worrying turn. A report by the Medicines and Healthcare products Regulatory Agency into the illegal sale of Melanotan on the internet shows increasing numbers are injecting themselves with an unlicensed product which has not yet passed the usual rigorous safety and quality tests.

The organisation, which also warned of serious safety issues around the use of needles to inject the substance, has now contacted 18 different websites advertising the product about the potential dangers. However, yesterday many of its users seemed unmoved by the news.

"It's given me the tan I wanted and so far I haven't had any problems," said one caller to a radio phone-in. "They don't know that there are any adverse side-effects. If there was, I think I would have felt something by now," added another, who admitted to having injected herself more than a dozen times over the space of three weeks.

Sold as Melanotan I and Melanotan II, the tanning product is designed to increase the body's levels of melanin, the natural substance in the body which gives skin its colour. Developed originally for the treatment of skin conditions, clinical trials are ongoing, but despite its easy availability it has not yet been licensed for human use.

"We are warning people not to use this product," says David Carter, head of the MHRA's medicines borderline section. "People are being fooled into thinking that Melanotan offers a shortcut to a safer and more even tan. It doesn't and the use of needles also raises issues of cross-contamination and infections.

"The safety of these products is unknown and they are unlicensed in the UK. The side- effects could be extremely serious and if anyone has concerns, they should immediately seek advice from their doctor."

Despite the awareness campaign, convincing those already using Melanotan that they should stop won't be easy. According to a recent survey, half the adult population say they feel healthier with a tan and many are prepared to go to any lengths to get it.

Each year, £40m is spent on sunbeds and tanning lotions and the phenomenon has led to a breed of tanorexics obsessed by achieving the perfect tan.

The history books say the origins of the current trend can be traced back to Coco Chanel. The fashion icon accidentally burnt while on a cruise to Cannes in 1923 and photographs of her deep tan spelt the end of the pale and interesting look.

However, it was the arrival of sun beds into the UK in 1977 which caused the mild fad to spiral. If a fortnight's holiday on the East Coast failed to provide a bronzed glow, there was always the local tanning salon to fall back on. Suddenly, having a tan during the summer months became not just desirable, but a necessity.

Latest research shows that many regularly ignore recommendations not to exceed 20 sunbed sessions a year and since the late 1970s the number of cases of skin cancer has more than doubled.

An estimated 70,000 people in the UK are diagnosed with the disease each year. Of these, 2,000 die and of those, 100 are thought to be the direct result of sunbeds and tanning lamps. The prognosis for the future looks similarly bleak. By 2020, experts predict the number of cases will have hit 300,000.

"Young people are constantly warned about the dangers of binge drinking and unprotected sex, but not enough is being done to warn them about the dangers of too much exposure to the sun," says a spokesman for Cancer Research UK. "Unless young people change their habits we could be heading for a skin cancer timebomb. Sadly, people still associate having a tan with feeling healthy and looking beautiful and that is the biggest hurdle we all have to overcome."