The results of the anonymous screening programme could lead to approval for the distribution of condoms in prisons, and, more controversially, clean needles for drug users.
The Home Office and prison authorities have been criticised for not taking measures to stop the spread of HIV among inmates at high risk, such as male prostitutes and drug addicts. Ministers do not want to be seen to condone behaviour involving homosexual acts or drug use, or to accept that illegal practices take place in British prisons.
However, if the spread of HIV was found to be significant, attitudes would change rapidly. Part of the problem has been that the numbers of inmates known to carry the virus is small - less than 50 - although this is acknowledged to be an underestimate. A voluntary programme at a prison in Edinburgh found that 4.5 per cent of prisoners were HIV-positive.
A spokesman for the Department of Health said yesterday that prison screening was a natural extension of the studies that have been carried out in ante-natal and genito-urinary clinics, and among the newborn. The official line is that it will lead to better services for HIV-positive prisoners and better targeting of health education.
Blood or saliva samples taken from prisoners in Wormwood Scrubs, Pentonville and Belmarsh prisons will be used.