Originally Posted by Monty
a shot gun or an air weapon shall be deemed to be loaded if there is ammunition in the chamber or barrel or in any magazine or other device which is in such a position that the ammunition can be fed into the chamber or barrel by the manual or automatic operation of some part of the gun or weapon
Cut and pasted from the act so this is the definitive answer!
Plus the additional stuff about reasonable excuse per Brians post above
That's the definition of what 'loaded' means, but there isn't actually any section in the act that says it's illegal to have a loaded air weapon where it would be legal if it was unloaded.
In short... the law doesn't care whether it's loaded or not.. If you've got a lawful excuse to have one in a public place, then it is still legal to have it in a public place even if it's loaded!.
Your car is a public place by the way..
So.. although it's not illegal to have your gun in the car with a loaded magazine in the gun - it's still very bad gun safety.