Where once getting hold of illegal anabolic steroids meant visiting a dodgy gym in a bad area of town, now it is as quick and simple as ordering the latest Harry Potter book.

You want the EPO you keep reading they are using in the Tour de France? No problem. Like to try some human growth hormone which the world's top sprinters are rumoured to be taking? Easy. Fancy some anabolic steroids to help build up your pecs? Enter your credit card number and we will ship them to your home address.

This week's case concerning the Great Britain rugby league international Keiron Cunningham is only the latest in a series of drug scandals involving some of the biggest names in sport. The man rated the best hooker in the world joins a long list of iconic stars to have been implicated in a doping controversy.

If past history is any guide, however, the biggest winner will probably be the manufacturer of HCG, the drug for which Cunningham tested positive after it was given to him without his knowledge.

"We couldn't ship the stuff out of the warehouse quick enough after all the publicity involving British athletes and [the anabolic steroid] nandrolone a couple of years ago," said a salesman for one company, who wished to remain anonymous.

"People suddenly thought it was a magic elixir. It is the same with EPO and the Tour. We don't stock it because it's a prescribed drug, but if we did we would make literally millions judging by the number of inquiries we get about it. Sunday cyclists seem to think it's going to turn them into a world champion overnight."

Although most are banned in Britain and by the International Olympic Committee, hundreds of these performance-enhancing substances are just a mouse-click away on the internet, which has made them more readily available than ever.

Some are relatively harmless, others can have serious effects on a competitor's reputation and health.

One of the leading drug advice sites on the internet, for example, warns of the dangers of taking HCG. It could lead to "reinforcing already existing breast growth in men" and "mood swings and high blood pressure".

At a press conference in London tomorrow, UK Sport's head of drug-free sport, Michele Verroken, will announce the results of the latest drugs tests for the quarter ended June 30 2003. There will be details of competitors who thought they could outwit the dope-busters, failed and were caught.

Much more worryingly, there will not be any information on those who thought they could get away with it and succeeded. For the drug war is a race where the cheats always try to stay one step ahead of the authorities.

Today, the industry is increasingly hi-tech: a complex, super-specialised smorgasbord of "designer" drugs. The relative few cases in Britain involving HCG - Cunningham is among only a handful to have tested positive for the drug - may make it seem to be the cutting edge of doping technology.

In fact, those in the know already consider it passé and are now using another drug, clomid, which offers the same benefits but is harder to detect.

Another example of how the cheats can steal a march on the dope-busters came during the 2000 Sydney Olympics when there were rumours some competitors were using an anabolic steroid called ganabol, which the IOC did not have a test for.

Scientists were baffled because the drug had been discarded by laboratories years earlier on account of its high toxicity. But in clinical tests in 1967 involving rats, ganabol had been shown to develop huge muscle growth, making it attractive to competitors in the power events such as swimming and sprinting.

The fact that some athletes had been using it was confirmed in 2001 by Charlie Francis, Ben Johnson's former coach, when he wrote about ganabol in an article for Testosterone Magazine.

"This drug was brought to the attention of the drug testers in 1984, but as it wasn't in commercial production a test wasn't developed for it," Francis wrote.

"Once athletes became aware of this loophole, a market quickly developed for the drug ... By the time a test was developed, the word was out and the athletes moved on to other products."

Ganabol is generally considered to be among the first of what are known as designer steroids, where the drug has its chemical structures modified so it is undetectable in urine tests but maintains its performance-enhancing qualities.

In his 2001 article, Francis claimed clandestine labs around the world were already working on finding the next designer drug that cannot be detected in time for the 2004 Athens Olympics. Few doubt they have succeeded.

The top names may have moved on but coming behind them will probably be a whole lot of eager new customers, armed with a computer, access to the internet, a credit card and warped sense of ambition, only too willing to click on for the chance to emulate their tainted idols.

How to abuse the system

HCG
What it's for: to treat infertility in males. Found in pregnant females.
What athletes use it for: to increase testosterone. To help them recover from injury.

Human gene therapy
What it is used for: to develop new body parts for transplants. What athletes use it for: not on the market yet but set to be the next big thing. Athletes already looking for the formula.

EPO
What it's for: to treat seriously ill kidney patients.
What athletes use it for: to boost oxygen-carrying red blood cells and increase stamina.

Human growth hormone
What it is used for: to treat underdeveloped children.
What athletes use it for: to increase muscle mass and strength. Very popular because it is almost undetectable.