Crown copyright exists in works 'made by Her Majesty or by an officer or servant of the Crown in the course of his duties' which includes material created by civil servants, ministers and government departments and agencies and includes material such as legislation, government codes of practice, Ordnance Survey mapping, government reports, official press releases, government forms and many public records.
Most material should feature a Crown copyright statement © Crown copyright.
Crown copyright work which has been published will have copyright protection for 50 years from the end of the year in which the work was published.
Unpublished works have a period of protection of 125 years from the end of the year in which the work was made or until 31 December 2039 (which is 50 years from the year in which the Copyright, Designs and Patents Act 1988 came into force).
Copyright in a work which has been assigned to the Crown lasts 70 years after the death of the person who created it.
The 'use and reuse' of Crown copyright material is managed by the Open Government License see: http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/