Britain's drug watchdog has reversed a controversial decision not to fund a new prostate cancer pill that was developed in the country after maker Johnson & Johnson agreed a new discount on supplies to the UK state healthcare service.

Zytiga, which is known chemically as abiraterone, was approved last year in Europe and the United States to treat advanced prostate cancer in patients who previously received chemotherapy.

The drug was developed by researchers at the Institute of Cancer Research and London's Royal Marsden Hospital. British pharmaceutical firm BTG is entitled to receive royalty payments on the drug.

The rejection of the drug in February in draft guidance from Britain's National Institute for Health and Clinical Excellence (NICE) on cost grounds drew unprecedented criticism from Cancer Research UK, a charity that supported research into the drug.

NICE Chief Executive Andrew Dillon said on Wednesday that the about-turn came after Janssen, a J&J unit, provided more details on the benefits of the drug and likely patient numbers, as well as the level of discount.

"We are very pleased that Janssen's submission to our consultation means we are able to produce draft guidance recommending abiraterone - it is an effective treatment, potentially extending life by more than three months, and it also allows patients to be treated at home as it can be taken orally," he said.

Harpal Kumar, head of Cancer Research UK, said: "This is wonderful news for patients with advanced prostate cancer and, in part, this U-turn is down to the public's disappointment at the initial refusal."

Alan Ashworth, chief executive of The Institute of Cancer Research, also applauded the decision.

"We are very pleased and proud that a drug we discovered will now be available to help many more people than before," he said.

"This success highlights the important role that not-for-profit organisations can make in drug discovery and development."

The drug has a list price of 2,930 pounds for a 30-day supply of 120 tablets, NICE said.