Two UK-based academics have devised a way to invent new medicines and get them to market at a fraction of the cost charged by big drug companies, enabling millions in poor countries to be cured of infectious diseases and potentially slashing the NHS drugs bill.

Sunil Shaunak, professor of infectious diseases at Imperial College, based at Hammersmith hospital, calls their revolutionary new model "ethical pharmaceuticals".

Improvements they devise to the molecular structure of an existing, expensive drug turn it technically into a new medicine which is no longer under a 20-year patent to a multinational drug company and can be made and sold cheaply.

The process has the potential to undermine the monopoly of the big drug companies and bring cheaper drugs not only to poor countries but back to the UK.

Professor Shaunak and his colleague from the London School of Pharmacy, Steve Brocchini, have linked up with an Indian biotech company which will manufacture the first drug - for hepatitis C - if clinical trials in India, sponsored by the Indian government, are successful. Hepatitis C affects 170 million people worldwide and at least 200,000 in the UK.

Multinational drug companies put the cost of the research and development of a new drug at $800m (£408m). Professors Shaunak and Brocchini say the cost of theirs will be only a few million pounds.

Imperial College will hold the patent on the hepatitis C drug to prevent anybody attempting to block its development. The college employs top patent lawyers who also work for some of the big pharmaceutical companies.

Once the drugs have passed through clinical trials and have been licensed in India, the same data could be used to obtain a European licence so that they could be sold to the NHS as well.

Professor Shaunak says it is time that the monopoly on drug invention and production by multinational corporations - which charge high prices because they need to make big profits for their shareholders - was broken.

"The pharmaceutical industry has convinced us that we have to spend billions of pounds to invent each drug," he said. "We have spent a few millions. Yes, it will be a threat to the monopoly that there is.

"I'm not only an inventor of medicines - I'm an end user. We have become so completely dependent on the big pharmaceutical industry to provide all the medicines we use.

"Why should we be completely dependent on them when we do all the creative stuff in the universities? Maybe the time has come to say why can't somebody else do it? What we have been struck by is that once we have started to do it, it is not so difficult."

The team's work on the hepatitis C drug has impeccable establishment credentials, supported by a grant from the Wellcome Trust and help and advice from the Department for Trade and Industry and the Foreign and Commonwealth Office.

But the professors' ethical pharmaceutical model is unlikely to find much favour with the multinational pharmaceutical companies, which already employ large teams of lawyers to defend the patents which they describe as the lifeblood of the industry.

One industry insider envisaged legal challenges if the new drugs were not genuinely innovative. It could become "a huge intellectual property issue", he said.