M1 when not really used by UKF infatry in combat.
You can always create a "new version" of the weapons and give it historic name like:
Rifle, No. 4 Mk I
Rifle No. 5 Mk I (although that looked different)
one also has to note that there is an used weapon already in game, although the weapon saw little action (mayby and idea for infiltration commandos):
De Lisle Commando carbine
As you can see in the picture, i do create a my own version of the scope enfield with a G43-like profile, and they still use it in the published version of my mod. The switching to M1 garand is an experiment and they have the same custom profile. My thought is that the M1 is more realistic with a semi automatic rifle profile than a scope enfield and taking historically, although limited, the british do use M1 garand rifle in some unit like the royal marine commando.
The delise carbine weapon do exist in the game in form of a profile, but it use G43 animation so nothing special.