One in seven men on the capital’s gay scene are thought to be infected with HIV – markedly higher than the rate for the general gay male population.

Although Health Protection Agency figures estimate that one in 20 gay men nationally and one in ten in London are living with HIV, a recent sample of 1,251 men in gay bars and clubs found that 15.2 per cent were carrying the virus.

Health experts believe that up to a quarter of gay men with HIV do not know they are carrying the virus and suggests that many wrongly think HIV-positive men can be identified through their appearances or how they act.

Alan Wardle, head of health promotion at sexual health charity Terrence Higgins Trust, said: “Men who have seen the campaign in focus groups have been genuinely shocked by the one in seven figure. Yet the reality is that, after Brighton, London has the highest HIV prevalence of any city in the UK.

“Many gay men wrongly believe that you can tell someone’s HIV status by what they look like, how they act, or who they’re friends with. But you can’t tell whether someone has HIV by looking at them, and with a quarter of gay men who have HIV currently undiagnosed, he may not even know himself.

“The assumption that HIV is visible is almost certainly affecting whether men use condoms or not. Forty-seven per cent of gay men surveyed reported having unprotected anal sex with at least one partner, and a quarter reported doing this with more than one casual partner. With this in mind, it’s vital this campaign reminds men that the best way to protect themselves and others is to use condoms.”

To highlight the figure and encourage men on the scene to use condoms, THT is running an advertising campaign in London gay magazines, bars, clubs and sexual health clinics over the next three months.