As we were alerted in a comment by Nick Holmes last year at this time, the U.K. has gathered together in one place nearly all of its online legislation. Legislation.gov.uk is managed by Her Majesty’s Stationery Office, in turn part of the U.K. National Archives. At the moment the site is still lacking a promised "changes to legislation" function that will chart the various amendments, repeals, etc. to legislation occurring since 2002. There is, however, a point-in-time search facility.
Curiously, I've been unable to find a statement on the site as to whether the online version of legislation can be regarded as authoritative.
From what I can tell, the search function permits you to search for terms within the title only. There does not appear to be a full text search function on the site.