most of this remains valid but has been amended:
Anti social behaviour act 2004 amends the “100 or more” people to “20 or more” people; and removes the loophole “in the open air” so indoor parties can be stopped under CJA powers.
HMSO no longer sell Government papers to the public; this bit of their functions has been privatised into The Stationery Office Limited (TSO). Most big bookshops have a TSO section, which can order this stuff for you. Most of it is available on the web anyway nowadays