For Sourabh Ghosh, it was nothing less than a matter of life or death.

Diagnosed with leukaemia more than a decade ago, the Delhi student was able to obtain a life-saving but expensive Swiss-produced medicine, firstly through a donation scheme and later through his medical insurance while studying in the US.

But when he returned to India in 2008, he was told he would have to pay for the drug. His salvation came in the form of a copy-cat medicine manufactured by an Indian company at a fraction of the cost.

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“It would have been a disaster if this alternative was not available. If I stopped taking medicine the leukaemia would have relapsed,” said Mr Ghosh, now a professor at the Indian Institute of Technology. “If you don’t treat it, it becomes aggressive. The patient will die after six to eight months.”

Mr Ghosh, 40, was on Monday among millions of people around the world celebrating a decision by India’s highest court not to grant a patent to a drugs manufacturer in a case campaigners say will help safeguard the ability of patients to afford life-saving medicine.

In a landmark case, the supreme court rejected a patent application by Novartis AG for a drug it claims was an updated anti-leukaemia treatment. Activists said the judgement would protect India’s £17bn generic drug industry, which makes cheaper imitations of life-saving medicine.

The dispute involving Novartis, a Swiss-based multi-national pharmaceutical company, dated back seven years and centred on its attempt to seek a patent for its anti-cancer drug Glivec. Glivec, which has been celebrated as a breakthrough in treating forms of blood cancer, costs £1,700 a month in its branded form while the generic version is available in India from £115.

The company claimed the drug was a new product while activists said it was merely a slightly modified version of an earlier product whose patent had expired.

Activists said today’s ruling means other drug companies will also be prevented from obtaining patents on updated version of exiting drugs, a practise known as “ever-greening”. They said the impact will be felt around the world.

Pratibha Singh, a lawyer for generic drug producer Cipla, part of an industry that is expected to be worth £46bn by 2010, told the AFP that the “ruling will have implications not just for India but also for other Asian, African and Latin American countries”.

She added: “The ruling also makes it clear you cannot patent a drug by just making some minor modifications — the key Section 3d of the patent law has been upheld by the court.”

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Mr Ghosh started taking Glivec after he was diagnosed with chronic myeloid leukaemia, a cancer of the white blood cells, in 2000.

While he was for some years able to access the drug through a donation scheme, since 2008 Mr Ghosh has been taking a generic version of the medicine. He will have to take it for the rest of his life. “I am doing perfectly well. I play sport, I swim,” said Mr Ghosh.

India’s generic drugs industry supplies around one-fifth of the world’s imitation drugs. It assumed this position because until 2005 it did not issue patents on drugs and only did so to comply with World Trade Organisation rules.

Novartis and other drug manufacturers argue that patents are required to protect products that have required large sums in development research and testing.

“We brought this case because we strongly believe patents safeguard innovation and encourage medical progress, particularly for unmet medical needs,” said Ranjit Shahani, of Novartis India Limited. “This ruling is a setback for patients that will hinder medical progress for diseases without effective treatment options.”

Novartis’ application for a fresh patent in India was turned down by the country’s patent office in 2005. It then filed an appeal, saying that the new product could be more easily absorbed and therefore qualified as a new product. That appeal was in turn rejected so the company turned to the supreme court.

Kiran Hukku of the Cancer Patients Aid Association, said over the last three years it had helped provide generic drugs to around 5,000 cancer patients who were still alive as a result of the medicine. “So many lives will be saved as a result [of today’s ruling],” she said.

Vikas and Preeti Ahuja were also celebrating Monday’s decision. Both have HIV and need to take two daily treatments of lamivudine, nevirapine and zidovudine. They receive their drugs from the Indian government, which purchases them from a generic manufacturer, again at a fraction of the normal cost.

Mr Ahuja, who was infected via a blood transfusion when he was a student and who is chairman of the Delhi Network of Positive People, said he regularly sent packages of such generic drugs to places such as China, Vietnam and even East Timor, where they are not available.

He said: “I would have been dead a long time ago without the generic treatment. If this decision had gone the other way it would have been a disaster, and a prolonged disaster. It would have affected future generations.”