Information on the average time served by first released lifer prisoners from all prison establishments in England and Wales in each year since 2000 can be found in the following table.
Mean time served (in years) 2000 13 2001 13 2002 14 2003 15 2004 14 2005 14 2006 14 Note: Table taken from table 10.5 of Offender Management Caseload Statistics 2006 http://www.justice.gov.uk/publications/prisonandprobation.htm
If released, life sentence prisoners are on licence for the rest of their lives and liable to recall at any time.
These figures have been drawn from administrative IT systems, which, as with any large-scale recording system, are subject to possible errors with data entry and processing.