The Town and Country Planning (Local Development) (England) Regulations 2004 are a statutory instrument that sets out the specific local development documents which local planning authorities in England are required to prepare and how that should be done.
Essentially the Act gives detail to the British Government's revisions to the planning system by means of the Planning and Compulsory Purchase Act 2004.
It came into force on the 28th of September 2004.
References
Town and Country Planning (Local Development) (England) Regulations 2004 Wikipedia(Text) CC BY-SA