Early Machmeter–What Aircraft used it?

This Machmeter is a puzzle to me, never been able to work out what Aircraft it would have been fitted to. And I’ve never seen or heard of one of these ever. It appears to be British Military from the late 1940’s, ( The Kings Crown is embossed on Elect Connecter at rear ) The 2 Pitot pipes are solid thick brass,mounted on a tufnol plate and unit itself is 4-3/4″ long with a 3″ Glass front face.
The Orangy looking bezel seems to be geared to that small lower Sub-Scale( which is seized ) Unit has no part no’s or Sect/Ref’s but in the black inner face just above centre is punched in ( very small ):- 41/4267 and unit weight is:- almost 2lbs.

The centre Screw Adjuster in middle of glass front seems to have been able to re-set a (What is now corroded ) wire pointer,that turns in to main face, but not quite touching it. and there is a metal stop also on main face, just under the white needle

No way this was made in 1941, surely not ???? Would the Gloster Whittle Jet developers have known about Compressibility effects at that time ???

Purchased off e-Bay a few years ago because of what it is, still none the wiser.—lol

This intrigues me,—- my tame Instruments man has no idea either, so we turn it over to your collective Forum wisdom to identify. Thanks !!

Bill T.