Looks like the time before the election, 25 May to 10 June 1987 when the aircraft was based in the Redhill Hangar, under armed police guard. Maggie was never seen there, the aircraft used to depart and pick her up somewhere else, I guess Battersea Heliport, but am not certain.
That was the time I showered an armed policeman in Hydraulic fluid, most embarrassing.
We got a thank you letter from her office.