There is a great deal of uncertainty about the prevalence of HIV in the UK prisons. The Department of Health's 1997/8 anonymous serosurvey is widely regarded by the Home Office as a benchmark study of HIV prevalence in prisons (Department of Health). Prisoners in eight of the 135 prisons in England and Wales were surveyed to determine the prevalence of and risk factors for transmission of blood-borne viruses in prison. Among the 3 930 tested, nine men and five women prisoners tested HIV-positive, giving an overall infection rate of 0.32% and 1.2% respectively.

In Scotland there are 4 303 people living with HIV according to Health Protection Scotland April 2005. The official HIV rates mirror those in England with a male inmate prevalence of 0.3%. The female HIV-positive rate was put at 0.6%.

Most observers agree that the Home Office numbers are under-reported; 0.32% translates to just over 200 English prisoners with HIV. Given that a quarter of people living with HIV are unaware of their status, this alone would boost the figures, and since inside prison stigma and discrimination are a daily fear, inmates have a high incentive to neither to be tested nor to disclose their status.

The official HIV infection rates are "The tip of the iceberg" according to a report in The Guardian (Allison 2005). An ex-prisoner told The Guardian that while he was in Lilttlehey prison, 32 prisoners were sharing one set of drug injecting equipment made from a ballpoint pen and a diabetes needle.

He said: "Of those 32, four were HIV-positive. By the time I left that nick, all 32, the whole shooting match, had contracted the virus." He claimed that in two prisons over twelve months he met "at least two dozen" HIV-positive prisoners who had not disclosed their status to prison staff.

The hepatitis C rates in the prison system are also disproportionately higher than the wider population. The Hepatitis C Action Plan for England, published by the Department of Health in July 2004, estimated that 0.5% of the general population in England (approx. 250,000 people) has been infected with hepatitis C, but that 8% of the prison population is believed to be infected - more than ten times the rate of general population. The incidence of hepatitis C in Scottish prisons was put at 8% among male prisoners and 14.8% among female prisoners (Gore). However according to the Hepatitis C Action Plan for Scotland 2005 it is suggested that as many as one in five prisoners in Scotland are hepatitis C positive.

The Action Plan says that there is variation in the current delivery of care across the country for people with hepatitis C. "Some groups of the population suffer from these inequalities more than others. There is a higher prevalence of chronic hepatitis C among prisoners because the majority (60%) of injecting drug users pass through the prison system at some point. A window of opportunity exists while they are in prison to take preventative action and improve their access to healthcare services."

One study of blood-borne viruses in British prisons concluded that "Good research informs. The British drugs policy in prisons needs academic credibility not credulousness or political spin" (Edwards). In Scotland the sheer weight of numbers of blood-borne transmissions has forced the prison authorities to react with pragmatic programmes of prevention. In England and Wales determining accurate levels of infection is a vital platform for prisoner health care. The Northern Ireland Prison Service, however, claims to have "no incidence of HIV in its prisons".