I might be able to date that photo (post #1111) precisely. My log book shows I was an F/O on Merchantman GAPEP ex GLA that diverted into LTN due LHR fog on 1st Feb 1973 (arr LTN 0025 on the 2nd). I remember at least one other VC9 there too - possibly the other one in the photo. If so the photo can be dated 2nd Feb 1973 - the day they returned to LHR.
The 'new' BEA paint scheme first appeared in 1968 on the Trident fleet - the jokers said it looked like the Union flag was being sucked into the intake of the centre Spey. Vanguards and Merchantman were gradually repainted over the next few years.