Undoubtedly the ramp scene is Southend. Because the aircraft are in BUA not Channel Air Bridge livery I would guess the date to be 1963 or just after.
Channel Air Bridge then later BUAF operated a joint venture service with SABENA for many years on SEN-OST with onward rail connections to Brussels. Two B170s were painted in SABENA colours but only one at a time carried that livery. They retained their British registrations and were flown by Channel Air Bridge crews and remained part of the CAB fleet.
The earlier shot of G-AICT must be Southend too, but not at the eastern end. The clue is the concrete slabs. In those days the only parking area at the south eastern corner was the old runway 33 which had a tarmac surface. My guess is we are looking at the BKS ramp and the pile of earth is on the north side of the main apron as a result of extension work. And in this location the cyclists would have been hidden from view of the tower by the ATL hangar, whereas in the south eastern corner they would have been in full view.
Well worth reading is "Air Ferry" by Douglas Whybrow who was GM of Channel Air Bridge in those days.