They say they were screened for the hepatitis C virus but not properly treated for the infection. Now they are demanding an explanation from the Department of Health and the General Medical Council, which polices doctors. Several hundred haemophiliacs were awarded no-fault compensation in 1991 for being unwittingly infected with HIV through contaminated blood products in the 1970s and 1980s.

They also had to sign legal waivers under the Department of Health deal, promising they would not sue if it was later found that they had hepatitis C as well.

Haemophilia Action UK, a group that has been campaigning, so far unsuccessfully, for an official inquiry into the contaminated blood disaster, says patients from round the country have only recently become aware of the fact that they had been "secretly" tested.

They have been demanding medical records from hospitals so they can prepare for legal action in the US against companies whose blood products were contaminated.

These suggest that they were tested for hepatitis C between 1990 and 1992, and that although many of the haemophiliacs were found to be positive, most claim they were not told until 1994. In some cases, doctors only informed them in 1998.

Carol Grayson, chairwoman of Haemophilia Action, has written to health ministers in protest. Hepatitis C was only formally identified in the 1980s, although doctors were aware of a mystery virus for years before that.