Team Sky cyclists used the sex pill Viagra at altitude to establish whether it had performance-enhancing benefits.

Sportsmail understands the drug was tested at a training camp for endurance riders while the team was in its infancy, following its foundation in 2010.

At least one rider was prescribed the drug by their personal GP, although it is not known for what reason. It is also believed a British Cycling staff member was prescribed the impotency drug for personal use by a team doctor.

Team Sky tested the sex pill Viagra at a camp in their search for marginal medical gains

Team Sky tested Viagra at an altitude training camp while the team was in its infancy

The performance-enhancing benefits of Viagra in the bedroom are well documented but some anti-doping experts believe it can also work to an athlete's advantage in the sporting arena.

Sportsmail understands Team Sky tested Viagra while the team was in its infancy and before Bradley Wiggins claimed their first Tour de France win in 2012, suggesting a willingness to explore the possibility of its performance-enhancing uses.

Viagra is not on the World Anti-Doping Agency banned list, so no athlete is under suspicion of having committed a rule violation. But there have been campaigns in the past to prohibit its use by athletes.

Don Catlin, an American anti-doping expert, suggested several years ago that Viagra could be used to enhance athletic performance. 'I thought there was some reason to be concerned about it and to put it on the (banned) list,' he said.

'There are credible scientific reports to show it is performance-enhancing in some circumstances, so I think it should be banned.

'There are also side-effects for people who don't have a legitimate medical need, so it's not a good idea for cyclists to try it without doing a study on it beforehand.'

No athlete is under suspicion of having committed a rule violation over the Viagra use

Victor Conte, who ran the Bay Area Laboratory Cooperative, which supplied banned drugs to leading US athletes, including runners Marion Jones and Dwain Chambers, told Sportsmail: 'I gave my athletes Viagra back in the day. We used to call it Vitamin V.

'I think it definitely has performance-enhancing benefits. It relaxes the walls of your cardiovascular system and improves blood flow.

'If you have a garden hose which you expand the diameter on it will allow more water to flow through. It's the same with blood flow and oxygen round your body. That's what Viagra does.'

Michele Verroken, the founding director of Sporting Integrity and a former head of Drug-free Sport, said: 'The effect of Viagra is to open up the blood vessels so the blood will flow better and oxygen will move to the cells more quickly.

Victor Conte, who ran the Bay Area Laboratory Cooperative, says he gave athletes Viagra

'There are those who say the theory is correct but nobody can prove it enhances athletic performance in practice.

'One of the general problems of sport is that people are looking for the edge with legal substances.'

Verroken suggested some doctors and sport scientists may be too quick to suggest legal drugs that could enhance performance. 'There's a lot of reflected glory in sport,' she said.

'They compromise their integrity by looking at the list of banned drugs and if something is permitted they think, "Why not?" That is where the culture of, "It'll be all right, it's not against the rules", comes from.'

Italian rider Andrea Moletta was suspended in 2008 when Viagra pills were found in a car

There is a precedent for use of Viagra in cycling. At the Giro d'Italia in 2008, one competitor, Andrea Moletta, was suspended after his father's car was searched and syringes hidden in toothpaste tubes were found — along with 82 Viagra pills.

WADA considered adding Viagra to its banned list in 2008. It came after some endurance athletes reported it boosted blood flow to their lungs.

Christiane Ayotte, a scientist at a laboratory accredited by WADA, said in a 2008 report she regularly found Viagra and a similar drug, Cialis, in the urine samples of male competitors.

British Cycling and Team Sky declined to comment.