That sort of confirms my thoughts, that it was based around a Herald fuselage. The Herald fuselage has 10 large rounded cabin windows, and this appears to be the same. Whole tail/engine section is a mock-up, and the flight deck windows appear very much taped on. I'd like to see that landing gear and those sideways struts actually retract !
Aerodynamically the whole tail looks too small for the rest of the airframe (reminiscent of the MD-11 then
)
ATV studios of the time were in Borehamwood, just down the road from the Handley Page plant at Radlett.
Do you think Patrick Wymark was meant to be representing Sir Frederick Handley Page ?