The number of pupils at pupil referral units with special educational needs, either with a statement or without a statement, can be found in tables 1a and 1b of the ‘Special Educational Needs in England: January 2008’ Statistical First Release accessible via
http://www.dcsf.gov.uk/rsgateway/PB/SFR/s000794/index.shtml.
Information broken down further by type of need is not held centrally.