Mooncrest asks that the idea of BY was buying factory fresh 737s so extending the idea to order new 707-304Cs would have seemed logical - but the 707C order heyday in 1971, as WHBM says was almost over - BOAC had just taken its last new 707C, G-AYLT to replace the SVC-10 lost at Dawson's.
Although BCAL formed in 1971 had agreed that their front line long haul aircraft was to be the 707C over the VC-10.
The early 70s was a time when the 720B, 320, 420, and even the better 320B and 320C 707s were appearing on the used market, offloaded as their owners upgraded to wide body jets.
Laker already had, in 1969, a pair of 707-138B's flying for Lord Bros and Group charters.
Caledonian AW had by 1969, a fleet of 7 new or almost new 707C's - Global, Tartan Arrow, Whitehall, Pontinental, and Horizon Holidays were big charterers of Caledonian 707's.
In 1970/71 Dan Air, Lloyd International, and BMA all obtained a pair of old ex Pan Am -321's for IT's and Affinity Group (to become ABC) charters. (Donaldson would also obtain 4 -321's).
All of the above were to be seen in Tenerife, Alicante, Ibiza, or Palma and they of course, also flew to the Far East/USA/Canada as was the norm.
BEA Airtours from 1971 for Enterprise, Flair, Thomas Cook and Martin Rooks Holidays, took on eventually 9 or so ex BOAC 707-420's, but KT had wanted ex AA 707-123B's but HM Govt and/or the BofT said no.
By 1971 Monarch had bought their first 3 720B's for Cosmos, which they used afar as St Lucia (for Pegasus Holidays) via the Azores iirc. They would also add 707-123B's to enable longer range.
Channel AW was looking at Continental 707's.
As mentioned, the 2 BRITANNIA 707's were used on IT's to the Med and the Canaries but they also flew for Thomson Holidays to MBJ Montego Bay, as well as on the Affinity Group T/A flights. Not sure what the KUL operation was - It may have been the jet-ship charter operation for LON to Australia for The FETC. Sabre Air took that on from LGW to SIN.
Both 707 though would soon end up at BCAL.
I was aware that Court Line looked at the DC-8 63 but I never heard that Britannia had.
Lloyd International had an order for 3 brand new DC-8 63PF's