Photo was taken from the then spectator area, with a buffet type restaurant I imagine.
AFAIK the cars are those of passengers and the some of this area remains the mid-term car park today. Can remember that area being turned into parking but when? - sometime between 1969 and 1973 I would guess.
Invicta also operated Boeing 720B G-BCBA out of Luton for a while- the only flight which I can remember both it and the Vanguards operating now with its callisgn was IM 555 which used to go to Rome. They did a lot of pilgrimage flights to Lourdes and picked up some IT work from other holiday firms like Jetway and Wallace Arnold when Court Line collapsed taking Clarksons with them so turbo propos re-appeared on the likes of Alicante which had become largely the preserve of jets by 1974.