More than half a million people in Britain may be infected with hepatitis C - two or three times the official estimates - a liver disease specialist warned on Wednesday.

William Rosenberg, professor of medicine at Southampton University, told APM he had alerted the Department of Health to his findings, which are based on a new mathematical analysis and are being submitted for publication.

He said the problem with the official estimates was they did not give enough weight to the way hepatitis C infection is clustered in high-risk groups and is virtually non-existent in other groups.

The new model assessed the prevalence of the virus among drug users, prisoners, healthcare workers, blood product recipients and people who had attended sexually transmitted disease clinics. The prevalence figures were then multiplied by the estimated number of people in these groups to give the overall population prevalence.

The results suggest that, as in France, somewhere around 1.2% of the British population may be infected compared with the 0.4% assumed by the UK Health Protection Agency.

“We are seeing twice the number of cases that we would expect if the official estimates were right,” said Professor Rosenberg, who also works as a physician at Southampton General Hospital.

He warned that action was needed to prevent a “huge epidemic” of people developing end-stage liver failure and requiring transplantation over the next 20 years.

“The problem is that many people look at these risks and don’t think it applies to them,” Rosenberg told the Independent newspaper. “But there is a huge cohort of people who 20 or 30 years ago may have dabbled in drugs, even just once at a party, who could be infected.

“They are the ones who could have had the virus for 20 or 30 years now and could soon start developing end-stage liver disease.”

So far, only 60,000 chronic carriers have been diagnosed in Britain and only 3,000 are receiving anti-viral therapy.

Last December, the health department launched a 2-million pound (2.9 million euros) campaign to encourage people who may have been exposed to the virus to get themselves tested.