Spam promoting medical treatments accounts for more than 10 per cent of junk email and is creating a "potent menace" to the health of UK surfers.

According to UK smart tags firm Flying Null, it is possible to purchase drugs online in response to spam without any medical checks or advice whatsoever.

Of the 8,301 unsolicited messages sent to a test email server during a three-month period, 849 offered drugs and medical treatments.

Email promotion of sex therapies such as Viagra was the most popular, accounting for 41 per cent of all drug and medical treatment spam.

Online pharmacies promoting a range of drugs, including Phentermine and Prozac, were the second most widely circulated form of spam, accounting for 37 per cent.

This was followed by weight loss, human growth hormones and anti-depressants.

Mark Gostick, business development director at Flying Null, said: "It is worryingly easy for consumers to prescribe themselves a poisonous cocktail of drugs by mistake. What's right for the average patient could be lethal to someone on heart medication."