Putting the clues together sofar, it appears to be an early Mk III.
The tailpipes are the 'thin' ones of the Welland.
The wingtips are the round ones of the Mk III, not the straight 'cut-off' ones of the Mk IV.
The cockpit represents the sliding canopy of the Mk III, not the side-opening one of the Mk I.
Thanks all already !
Any more clues will be most welcome, of course !