Remember you now have to keep it locked in an FAC standard cabinet
Not strictly true. In fairness, I didn't realise the law had changed but from the Crime and Security Act 2010:
"9. In many cases, this can be achieved by using an existing, suitably robust, lockable cupboard and by keeping the keys separate and secure. Alternatively, they could use a lock or locking device by which an air weapon can be attached to the fabric of a building, or to a fixed feature, or a security cord, lockable chain or similar device attached to a point of anchorage within the building."