Here is a detailed summary of the laws for Airsoft in the UK.
In United Kingdom There are currently certain restrictions on the possession of airsoft replicas, which came in with the introduction of the ASBA (Anti-Social Behaviour Act 2003) Amendments, which prohibit the possession of any firearms replica in a public place without good cause (to be concealed in a hard gun case or sealed container only not to be left in view of public at any time) . The prohibition of self-contained gas cartridge weapons similar to that made by Brocock can arguably apply to Moscarts and BB-Shower grenade systems, however a formal case precedent has yet to be set. There were initial concerns among the airsoft community that the Violent Crime Reduction Bill (passed an Act in November 2006, but not yet commenced) would in future prevent airsoft skirmishers from buying realistic imitation firearms. However, on the 20th of September 2006 the Association of British Airsofters (ABA) received a letter from Tony McNulty saying that he has "decided to provide a defence for airsoft skirmishing in relation to the ban on the sale etc. of realistic firearms". There has been confirmation airsoft will receive an exemption. This letter has been scanned and reproduced on the ABA website . Note that membership of the ABA may be required in order to view the letter.
Since then, the Bill has received Royal Assent, and while now Statute Law in the UK, is still a matter of some (at times heated) discussion in the UK Airsofting community - not least of which the question as to how the Act, and Specific Defence, will work, the process of which is still being decided upon at the Home Office, at the time of this edit (5th December 2006).
The Defence will be based on whether or not a person is a Skirmisher. One of the measures put in place by retailers to aid in identifying Skirmishers is a database of skirmishers registered in a central database. A person must be a regular skirmisher (i.e. skirmish 3 or more times in no less than two months) in order to be registered, and the airsoft site they register/skirmish at must hold public Public Liability Insurance. Once a skirmisher is registered they receive a membership card and must produce this before buying or trading airsoft weapons from these retailers, though not a legal requirement (As long as you can prove that you are an airsoft skirmisher you may purchase Realistic Imitation Firearms or RIFs. (Airsoft guns deemed to be realistic.) It is expected that HM Customs & Excise will also have access to the database to verify the identity of importers.
The VCRA (Violent Crime Reduction Act) came into effect as of the 1st October 2006, thus meaning that RIF (Realistic Imitation Firearms) can only be purchased by registered members of an airsoft skirmish site (accessories and ammunition are not covered by the VCRA). Only those people over the age of 18 can purchase Replica Imitation Firearms. IF (Imitation Firearms), however, are still legal and may be purchased by anyone 18 or over, regardless of membership status. These usually take the form of "Two-Tone" guns - normal Airsoft guns, that have been painted in bright colours in order to mark them out clearly as Imitation Firearms and not Realistic Imitation Firearms.