In 2003 the Home Office Research directorate reported that 2% of prisoners in the UK were injecting drugs. An earlier published in The Howard Journal Of Criminal Justice 1997, suggested that 6.7% of inmates injected drugs and that there were high levels of needle-sharing by prisoners who used intravenously.

Underreporting again has to be factored into the equation. Illegality and stigma surrounding intravenous (IV) drug use behind the walls of penal institutions make accurate estimates notoriously difficult. A survey in 2004 in Scottish prisons (Howie) reported that in 2003/4 6,500 random drug tests were carried out, one for each prisoner, and 32% of inmates tested positive for heroin use. About 25% were using cannabis.