I spent a month at Stansted in the mid-60s on a Met. Observers course. Apart from various airlines carrying out mainly circuit training.......constellations, vanguards 707s etc [what a mix!] the majority of movements were the Civil Aviation Flying Unit. At that time Doves and Princes in the 'Minair' red and black livery. Off they all went to carry out flight checks on en-route and airfield navaids and of course the ATC college at Bournemouth being a 'CAA' college in those days had some use of Minair aircraft for training airfield radar controllers.
The Manual of ATC stated that CAA flight calibrations had priority over most other aircraft and the 'calibrators' of the past twenty years have been far more cooperative than the Minair guys in this respect. The latter certainly demanded priority and in the days of the HS 748 calibrations made it very difficult to expedite and maintain an orderly flow of the other traffic, particularly when they failed to communicate their next intention!
It was a good day when 'regulation' and 'operations' were segregated!
H49