I've sped through this a bit quick so excuse if I've missed summat.
Brian is very much correct in his explanations.
To clarify magazine fed weapons. To be classified as 'loaded' the magazine MUST have at least one pellet in and MUST be fitted into the weapon. Magazines fully loaded away from the weapon, even in the same section of the bag - unloaded.
Under the current law the legal status of a loaded weapon may appear irrelevant, but as Brian has explained 'Reasonable excuse' is a coverall for the law and would encompass all the relevant facts of the alleged offence.
There will be very few occasions when you could justify having a loaded wepaon in the public arena; perhaps crossing a footpath whilst stalking on rural land would be acceptable, but you may have to persuade the magistrate.
From personal experience of being someone carrying a big pointy stick, dealing with a person carrying a small pointy stick; it's not okay to cross a council estate with a loaded air rifle at school kicking out time because you're " between woods"