Just for info - The Violent Crime Reduction Act 2006 (Realistic Imitation Firearms) Regulations 2007 make it an offence to have an imitation firearm - the definition of which is to be found in s.38 of The Violent Crime Reduction Act 2006 - whereby it states that a firearm which is realistic, and could only be identified as otherwise by an expert or examination is covered - so even a deactivated firearm may be covered. There are exemptions for historical re-enactments/shows etc
But having had a talk given by the police recently, the general enforcement opinion was that they may stop you and confiscate weapons because of this, unless you have all your paperwork with you etc..... so advice would be only have it on display if you are attending shows, and always carry deactivation certs with you etc.. Just thought you may like to know as no one has raised this legislation yet..
You can find all the legislation at the office of public sector information site at http://www.opsi.gov.uk or just enter into into a search on google