Can you walk around with an air gun in the UK?
According to Home Office guidance, it is an offence to have an air weapon in a public place without a reasonable excuse. The guidance goes on to say that “It is ultimately for the courts to decide what a reasonable excuse is. However, it might include carrying a weapon to and from a shooting club, or taking a new weapon home from a dealer.” If you have some sort of membership card, printed-out email, or other relevant documentation proving what you say, then this should be enough—although it may depend on the mood the officer is in at the time.