Britain is poised on the edge of an epidemic of liver failure caused by hepatitis C that could kill more people than Aids.

Britain is poised on the edge of an epidemic of liver failure caused by hepatitis C that could kill more people than Aids.

The virus, spread by blood-to-blood contact and, rarely, through sex, is estimated to have infected 250,000 to 500,000 people. Although symptoms are mild or non-existent in the early stages, 85 per cent become chronically infected and up to one in three of those is expected to develop cirrhosis in 20 to 30 years.

A survey of 5,000 women attending a London antenatal clinic found almost one in a hundred infected. The survey, published today in the medical journal Gut, is the largest done in an unselected population and, extrapolated to the whole country, implies 400,000 people may be infected.

Graham Foster, of the liver unit at St Mary's Hospital, London, who led the study, said many of those infected had contracted the virus through intravenous drug use years ago. They were mostly professional people who had dabbled in drugs in their 20s.

He said: "There has been a big increase in people coming to liver clinics but we ain't seen nothing yet, because most of these people became infected around 20 years ago. We are at the start of a massive surge of cases and we don't know how big it is going to be."

In the United States, 4.5 million people are estimated to be infected. If rates in Britain are at the same level, up to 800,000 people could face liver failure, most in their fifties.

Everett Koop, the former US surgeon general who has campaigned on the issue, said in April: "We stand at the precipice of a grave threat to our public health ... it affects people from all walks of life, in every state, in every country. And unless we do something about it soon, it will kill more people than Aids."

Unlike Aids, hepatitis C is treatable with a combination of the drugs interferon and ribavirin, which can cure 40 per cent of cases. But they cost £7,000 a patient and have to be taken for up to a year. Treatment involves three injections a week and has unpleasant side-effects - chiefly flu-like symptoms - which cause one in five patients to drop out.

Many health authorities refuse to pay for the drugs, exposing patients to the mercy of the postcode lottery. The issue has been referred to the National Institute for Clinical Effectiveness (Nice), which is to give its ruling later this year.

Howard Thomas, of St Thomas' Hospital, chairman of the Government's advisory group on hepatitis, said hepatitis C was its main focus. "We are working on the premiss that between a half and 1 per cent of the population are infected, between 250,000 and 500,000 people. We know this is a big problem and we are hoping Nice will make the treatment uniformly available across the country."

However, he said the case for screening was unproved, because the treatment, though effective in severe cases, remained to be demonstrated in mild cases. People with mild symptoms, who might never suffer liver failure, had to endure an unpleasant treatment, possibly for no benefit. Professor Thomas is co-ordinating a study of the drug treatment in mild cases in 12 centres in Britain, the results of which will be known next year.

William Rosenberg, of the liver group at the University of Southampton, says in an editorial in Gut, the gastroenterology specialists' journal, that the high level of infection shown by the study of pregnant women "establishes hepatitis C as a major healthcare problem for the 21st century and one that cannot be ignored".

In America the costs of treating hepatitis C over the next 20 years have been estimated at $85bn (£53bn). Allowing for the lower population and lower infection rate in Britain, that suggests costs here of $9bn. Dr Rosenberg said: "We can make a huge dent in that $9bn by spending something now. We can do a huge amount more about hepatitis C than we can about heart disease or hypertension of diabetes."

He added: "The idea that the typical hepatitis C sufferer is someone lying in the gutter injecting drugs is far from the truth. The majority are well-to- do, happy professional people who experimented with drugs in their youth and are paying the price."