This information is not collected centrally.
However, Her Majesty’s inspectorate of prisons (HMIP) and the Youth Justice Board publish an annual survey of children and young people in custody. The survey for 2008-09 involved 1,100 young people detained in 18 establishments across the secure estate. This reported that 24 per cent. of young men and 49 per cent. of the 54 young women in the survey had been looked after at some point in their lives. It is important to understand that that the overall number of children with a care background in custody is small relative to the total number of looked-after children above the age of criminal responsibility.
This report is available from the HMIP website at:
http://www.justice.gov.uk/inspectorates/hmi-prisons/index.htm