The Localism Act http://www.legislation.gov.uk/ukpga/2011/20/contents/enacted received Royal Assent on the 15th November, 2011. Different parts of the Act will come into force at different times, with some being brought into force immediately.
The Act is wide ranging, but brings into force two key provisions which will have an immediate effect for Gypsies and Travellers: the abolition of the Regional Strategies and the changes to the law regarding retrospective planning permission.
Section 123 of the Localism Act inserts new sections into the Town and Country Planning Act 1990 preventing retrospective planning applications where there is already an enforcement notice on the land which covers the subject matter of their proposed application. If there is not such a notice, then a retrospective planning application can still be made.
More info here: http://travellerspace-cornwall.blogspot.com/2011/12/what-localism-act-2011-means-for.html?spref=fb