On another website this was identified as an A-36. I disagreed on the basis of there being no apparent evidence of dive brakes and it's being on a photo ship. It does have nose guns however and I'm not sure P-51As had them:
It is neither an A-36, nor is it a P-51A; it is an RAF Mustang I, the first version of the Mustang built specifically for the RAF: this is AG633 of 2 Sqn, an Army Cooperation Squadron from the RAF's Army Cooperation Command which, in 1943, formed the basis of the 2nd Tactical Air Force.
(Kinzey, P-51 Mustang in Detail and Scale, 1996)
This is the RAF A-36 used as a trials aircraft; one small puzzle is that this A-36 looks as if it doesn't have the .50 cals under the nose, but closer inspection shows the blanked off gun ports.