RAF allows moustaches too.
Apparently "not to extend below the edge of the mouth" which still leaves quite a lot of room for expression I would guess.
Rule still applies while on secondment [1].
My Grandfather was born before the days of safety razors and tells me that Navy personnel were able to petition to avoid shaving on account of delicate skin (something about the salt water and fresh air). I think anybody who could grow a beard would have done.