ID of regiment from FS Cap and partial badge

[TomPC]

Dear All,

Please can anyone tell me what uniform this chap is wearing?

He is Maj. Anthony 'Andy' Robert Whately-Smith and served as follows:

1940 - Dorset Regt.
At some point - General Staff Officer (GSO3)
1944 - Briefly, Parachute Regiment
1944 - 2nd SAS

I believe his headgear is known as a field service cap. There is a smidge of badge showing. Is it possibly the Army Air Corps, which I think was the umbrella organisation housing the Paras and the SAS for a period during WW2?

Any help gratefully received.

With best wishes,

Tom