Healthy gay and bisexual men should be given a daily dose of the HIV drug Truvada to reduce their chances of contracting HIV, it has been suggested.
Scientists have discovered that talking the drug could reduce the risk of infection by 86%.
In a year-long clinical trial of 545 high-risk men, of the 696 men not given Truvada, 19 became HIV-positive.
Of the 273 who did take the drug, only two were infected.
UK Medical Research Council and Public Health England scientists compared Truvada to the pill for women, and denied that it would encourage risky sexual behaviour.
Doctor Anthony Nardone, one of the researchers said that the NHS should consider making the drug available and said: "I don't envisage all men taking PrEP [pre-exposure prophylaxis] for all their lives, but in effect what we're doing is giving men an option to get through periods of very high risk in their lives."
The result were described as a "game changer" by Doctor Michael Brady, the medical director of the Terrence Higgins Trust, who also urged the Government and the NHS to make the drug available.
"We know that most gay men use condoms most of the time, and that this has prevented tens of thousands of HIV infections since the epidemic began in the UK. However, we also know that condomless sex vastly increases the risk of HIV being transmitted," he said.
"It is not a vaccine and it won't be for everyone but, once approved, we expect it to significantly increase the momentum in our fight against the virus."
It is estimated that 100,000 people are living with HIV in the UK.
In London is believed that one in eight gay men in London is HIV-positive, compared with one in 26 in the rest of the UK.