A drug that dramatically reduces the chance of contracting HIV is to be offered free on the NHS from next month, it was announced today.

Sexual health clinics in London will be among the first in the country to offer the treatment, known as PrEP or pre-exposure prophylaxis, from early September.

It will be offered to about 10,000 high-risk people across the country under a £10 million three-year trial. Previous trials have shown it cuts the risk of HIV from unprotected sex by 86 per cent. Experts believe its availability could effectively end the HIV epidemic in the UK.

Deborah Gold, chief executive at National AIDS Trust, said: “This is a pivotal moment in the fight against HIV. PrEP, if targeted properly at those in need and at risk, offers the possibility of transforming the English HIV epidemic.”

The trial, the largest of its kind in the world, comes after the Court of Appeal last year ruled that funding PrEP fell within NHS England’s remit. It had argued that providing the drug was the responsibility of local authorities.

People have been able to buy PrEP privately at a cost of about £400 a month. It is normally taken as a daily pill. The NHS in Scotland decided in April to make it freely available.

There are about 2,600 new diagnoses of HIV in London a year, but campaigners believe the capital could be on the verge of a big reduction due to the use of PrEP and early testing.

The trial – which will also be pioneered in Brighton, Manchester, Liverpool and Sheffield – will be extended countrwide by next April. It will gather evidence on the uptake and cost-effectiveness of the treatment. Women and transgender people will also be given access to the trial.

Simon Stevens, chief executive of NHS England, said: “This major new intervention should complement and supercharge the wide-ranging and increasingly successful effort to prevent HIV. It’s another milestone in more than three decade’s worth of progress in tackling one of humanity’s major health challenges.”

Ian Green, chief executive of Terrence Higgins Trust, said: “We’re pleased that NHS England has announced a start date for the much anticipated PrEP trial. This trial has been gaining momentum in England, and is vital as we work towards ending HIV transmission.

“The priority must now be to make sure that the trial is rolled out speedily across the country, and that no-one at risk of HIV is left behind. Now that the PrEP trial drug has been procured, we’re well on the way to protecting over 10,000 people at risk of HIV.”

Professor Brian Gazzard, chief investigator for the PrEP trial, said: “This.. could mean the difference between staying HIV negative or becoming HIV positive. The data and evidence we generate will not only be of international interest but more importantly will enable commissioners in England to plan for a PrEP programme that benefits individuals and the taxpayer.”