Prior to the Anti-social Behaviour Bill the criminal law only covered under 14 year olds supervised by an over 21 year old and both parties were liable. In every other case firing beyond where you have permission to shoot is constructive trespass and comes under civil law. Under the new Bill, as the press release says, a 14-17 year old will now be liable under criminal law. Over 17 it is still a matter for the civil law.

Only guns using the self-contained air cartridge system become illegal without an FAC(ie Brocock).

The public place provision brings airguns into line with other firearms law covering shotguns, fac etc. Lawful authority is very literal - a police officer must tell you to carry that gun over there sir. Reasonable excuse is the main factor for everyone.

The airgun in the boot is a useful analogy - you would need to be transporting it somewhere for a purpose (shooting, going to the gunshop, taking it to show your friend to make him/her laugh/weep etc). Leaving it in the boot permanently would be a bad idea for many reasons.