Online dating apps are fuelling the risky practice of drug-fuelled “chemsex” at gay orgies in London, an investigation claimed today.

Sites such as Grindr, GROWLr and SCRUFF are making it easier for “men who have sex with men” to find sexual partners, amid concern at a rise in sexually transmitted infections in the capital.

A Radio 4 documentary told how drugs such as mephedrone, GHB/GBL and crystal meth were being taken at gay house parties to increase sexual appetite. But because these also lower inhibitions, they can lead users into “unintended unprotected sex”.

One 22-year-old Londoner, Jack, who has been experimenting with drugs for eight years, said: “Sex on crystal is like something else. You f**k like a porn star. It gives you that confidence.”

Another gay man, Kiran, who has used crystal meth, said: “What you would call ‘vanilla’ sex just doesn’t match up to it.”

Jack told the drugs enabled him to party from Friday night until late on Sunday. He only slept after returning from work on Monday. He might attend eight house parties at the weekend and have sex with up to 14 men.

Asked whether he feared contracting HIV, he said: “I have played with fire so much, if it happens, it happens. It isn’t the end of the world these days.”

Some men who indulge in chemsex advertise the fact on the smartphone apps by adding a pill logo to their profile. The move away from pubs and clubs to private house parties has sparked concern by putting users out of reach of sexual health and drug advice services.

Dave Stuart, of the Club Drug Clinic at 56 Dean Street, said: “These three particular drugs we are talking about are very powerful sexual disinhibitors for a population of people who need some disinhibition around their sex.”

Figures released last week by Public Health England revealed that sexual infections in London increased by five per cent to 113,381 cases. Among young Londoners, gonorrhoea was up 20 per cent to 4,341 cases. Gay men accounted for two-thirds of these cases and 90 per cent of syphillis cases among the same 15-24 age group.

HIV infections are also rising, with concern that the availability of anti-retroviral drugs such as Truvada encourages “bareback” (unprotected) sex. One in eight gay men in London is thought to have HIV.

* The Report is on BBC Radio 4 from 8pm to 830pm.