as for shooting in the back garden its not just the neighbors you need to worry about - say your practicing breakout and running and trip pulling the trigger letting of a volley over the fence into public space if u hit anyone - NOT good,
also most members of the public wouldnt know a firearm from a toy (let alone a paintball gun) so if someone sees you with a gun they could call plod,
and if your parents aint home your going to have fun trying to convince them you arent on your way out of the garden to shoot up the streets
unless youve just done maintenance and need to test id say dont fire in the garden