The test plane looks like a Miles Magister and the aircraft collecting the camera a Percival Gull. The bigwigs arrive in a DH89A Dragon Rapide.
The test aircraft carries the registration L6908, which is said to be an RAF Miles Magister Mk.I which crashed on 27 August 1941 at Chapel-en-le-Frith, Derbyshire (website of Peak District Air Accident Research). This seems to be the aircraft which features in most flight shots at altitude.
However, the tail-fin of the aircraft seen in one landing and in most ground shots differs in shape, and appears in fact to be the civil Miles M.2 Hawk Major.