The High Court in England has ruled that NHS England can indeed fund what campaigners are calling a "game-changing" drug that prevents the transmission of HIV, after health chiefs tried to hand over responsibility for commissioning the service.

Pre-Exposure Prophylaxis (PrEP) involves HIV negative people taking an antiretroviral drug to avoid getting the virus. Recent evidence indicates that the approach can be highly effective in preventing transmission of the disease as long as the drugs are taken regularly; data from the pilot phase of the PROUD study show that PrEP using Truvada cut the incidence of HIV infection by 86 percent.

Research funded by Public Health England (PHE) calculated that offering pre-exposure prophylaxis alongside regular HIV testing and early treatment to just a quarter of MSM at high risk of contracting HIV could prevent around 7,400 new infections (44 percent of total incidence) by 2020.

The once-daily pill costs around £360 a month, according to the AIDS charity the Terrence Higgins Trust, but it points out that this is still cheaper than the cost of treating HIV.

NHS England's stance is that it does not have the legal power to fund a national Pre-Exposure Prophylaxis (PrEP) service, and that this should instead fall under the remit of local authorities, as they control preventative health.

However, the National Aids Trust (NAT) argued in Court that there is no legal impediment to PrEP being commissioned by NHS England, and the judge agreed, concluding that both factions can legally fund the service.

"This is fantastic news. It is vindication for the many people who were let down when NHS England absolved itself of responsibility for PrEP," said Deborah Gold, chief executive of NAT.

"Over 4,000 people are getting HIV every year in the UK - we desperately need further prevention options to add to condom use. PrEP works. It saves money and it will make an enormous difference to the lives of men and women across the country who are at risk of acquiring HIV. The delay to commissioning PrEP is both unethical and expensive."

In his judgement, Mr Justice Green wrote: "No one doubts that preventative medicine makes powerful sense. But one governmental body says it has no power to provide the service and the local authorities say that they have no money. The Clamant is caught between the two and the potential victims of this disagreement are those who will contract HIV/AIDS but who would not were the preventative policy to be fully implemented."

However, NHS England has said it will appeal the ruling. "Queen's Counsel has advised that the Court's ruling interprets the legislation governing NHS England's role and functions in a way that is inconsistent with Parliament's intention," it noted.

The NAT said it is "enormously disappointing" that NHS England has decided to appeal the judgment, as it will "further delay clarity in this area, and mean that any potential commissioning of PrEP will not take place for months".

Commenting on the situation, Mike Thompson, chief executive of the Association of the British Pharmaceutical Industry, stressed that "consistency and clarity for the commissioning of medicines is vital," and that "patients and their families will now only face further delay in accessing a number of treatments for HIV, cystic fibrosis, cancer, and other life-changing treatments that continue to be clogged up in the system".