The Criminal Justice and Court Services Act 2000 gives new powers to courts to disqualify an individual who has committed a serious offence (s.26) from working with children (ss. 28 and 29). Breach of such an order will itself be a separate criminal offence. There is a long list of what amount to serious offences for s.26 purposes (see sch 4 to the Act).
These provisions were brought into force on 11th January 2001 by the Criminal Justice and Court Services Act 2000 (Commencement No. 1) Order 2000 SI 2000/3302.
There is general guidance on a Home Office website at www.homeoffice.gov.uk/cjcs/cjcsguide.htm.