The government is being urged to promote condom use

The Terrence Higgins Trust said the competition was a "magnet" for sexual activity and could lead to an increase in sexually transmitted diseases.

The charity urged the government to use the event to promote sexual health.

A spokeswoman for London 2012 said it was planning a health promotion drive before and during the Olympics.

The Terrence Higgins Trust said competitors at the 2002 Winter Olympics in Salt Lake City, Utah, used 250,000 condoms during a 10-day period.

And at the Sydney 2000 Olympics, an extra 20,000 condoms had to be ordered after the initial supply of 70,000 ran out, the charity said.

Unwanted pregnancies

Paul Ward, the charity's deputy chief executive, told the Health Service Journal that, with thousands of athletes and hundreds of thousands of visitors flocking to the games, organisers must promote sexual health - for example by making condoms easily available.

"Unless there's a very positive step taken to promote good sexual health we could see increasing levels of STIs (sexually transmitted infections)", he said.

"We have to have a strong focus at the time of the Olympics promoting condom use and promoting the risks of STIs.

Mr Ward said that, with unwanted pregnancies and STIs at an all-time high in the UK, the Olympics should be used to encourage condom use.

"Given that there will be a global focus to the Olympics, there is a good opportunity for the government to provide international leadership on HIV," he added.

A spokeswoman for London 2012 said: "We already have a Chief Medical Officer (CMO) and a Medical Services Manager in place who will be working on plans to address all aspects of sexual health for spectators, workers, volunteers and athletes at Games-time, as well as looking at anti-doping issues.

"The CMO will be putting a medical team in place and will be working closely with the NHS and other agencies in this area."