Wearing the uniform is not an offence. trying to pass yourself off would be the offence.
I say when playing soldiers who cares?
Not that someone claiming Parachute Wings or a Green Beret or wearing an SAS badge wouldn't look a tit.
Thousands of people regularly dress up in uniforms and insignia as part of a Re-enactment group and they even give themselves ranks, even award themselves Commissions.
No one complains about that but they are just as much playing soldiers as an Airsofter