At the end of November 2008, there were 83,423 prisoners detained in all prison establishments in England and Wales. This information is available from the following website, which is updated monthly:
http://www.justice.gov.uk/publications/populationincustody.htm
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.
The National Offender Management Service (NOMS) works with prisoners to address their offending behaviour and manage their risk of reoffending on the basis that they have been correctly convicted by the courts. As such, a central record of those who maintain their innocence following conviction would serve no useful purpose.
It is also open to any person who believes that they have been wrongly convicted to challenge the safety of their convictions through either the Court of Appeal or the Criminal Cases Review Commission.
Current guidance for Prison Service staff in dealing with prisoners who deny guilt is contained in chapter 7 of (Prison Service Order) PSO 4700 which is available at:
http://pso.hmprisonservice.gov.uk/pso4700/PSO_4700 _lifer_manual.doc