When going out stalking, I carry my ammo in an elasticated cartridge wallet separate from the magazine, though both items are in the same Haversack, Respirator, S10.
The only concerns I can see are:
1.
Legal. The law states:
19 A person commits an offence if, without lawful authority or reasonable excuse (the proof whereof lies on him) he has with him in a public place...
[
F5(a) a loaded shot gun,
(b) an air weapon (whether loaded or not),
(c) ...
any other firearm (whether loaded or not) together with ammunition suitable for use in that firearm, or
(d) an imitation firearm.]
An Act to consolidate the Firearms Acts 1937 and 1965, the Air Guns and Shot Guns, etc. , Act 1962, Part V of the Criminal Justice Act 1967 and certain enactments amending the Firearms Act 1937.
www.legislation.gov.uk
2.
The longevity of the magazine follower spring. With modern materials, and considering the times involved, I don't think that this is an issue worth considering.
I don't see a problem with either approach. Some might say that your method - mag & ammo completely separate from the rifle and in your immediate possession - is better from a public safety viewpoint. I find that having everything together makes life easier and brain farts less likely.
maximus otter