A High Court judge is to rule on whether a preventative treatment for HIV which charities say is a "game changer" should be funded by the NHS.
Mr Justice Green, sitting in London, has heard a challenge brought by the National Aids Trust (NAT) against NHS England.
The case relates to pre-exposure prophylaxis (PrEP), a "highly effective" anti-retroviral drug used to stop HIV from becoming established in the event of transmission.
When taken consistently, PrEP has been shown to reduce the risk of HIV infection in people who are at high risk by more than 90%.
A row erupted earlier this year after NHS England said it would not routinely fund the drug.
In March, the body decided the treatment was a preventative service and was therefore not its responsibility. It has said local councils are in charge of funding preventative health services.
However, NHS England agreed to a re-evaluation after the NAT launched a legal challenge.
Then in May it said it had "considered and accepted NHS England's external legal advice that it does not have the legal power to commission PrEP", and that under 2013 regulations "local authorities are the responsible commissioner for HIV prevention services".
It said if it prioritised PrEP there was the risk of a legal challenge from proponents of other "treatments and interventions that could be displaced by PrEP".
The NAT, an independent charity, challenged the May 31 decision to "exclude" PrEP from consideration by NHS England's Clinical Priorities Advisory Group "as part of its annual commissioning process".
It argued that the body does have the legal power to commission the drug.