[holding answer 21 October 2008]: The available data are given in the tables placed in the House Library.
The requested data are also published as part of the annual Police Service Strength England and Wales Statistical Bulletin. The 2008 bulletin can be found at:
http://www.homeoffice.gov.uk/rds/policeorg1.html
and previous years' bulletins are available in the House of Commons Library. The annual Home Secretary's Race Employment Targets report may also be of interest in relation to the question asked:
http://www.homeoffice.gov.uk/documents/race-equality-targets-2006-07