firearm," except where otherwise expressly provided, means any lethal barrelled weapon of any description from which any shot, bullet or other
missile can be discharged and includes any prohibited weapon, whether it is such a lethal weapon as aforesaid or not, any component part
of any such lethal or prohibited weapon, and any accessory to any such weapon designed or adapted to diminish the noise or flash caused
by firing the weapon;
The Met (firearms qualified officer serving in SO**) have told me that a magazine is not a "component part", Lothian and Borders have told me that it is (and let me off with an unofficial caution for having 4 in my luggage).