Certainly in 1971 summer G-AYSI was based at Manchester and operated high-intensity IT flights to The Med etc. The Thomson Sky Tours holiday brochure for the season was pretty detailed about flights and times and which ones were operated on the 707.
The capacity was fine in July and August weekends, but outside these times they were rather too large. They also picked up various affinity Transatlantic charters, but it was notably competitive and the margins were just not there - many UK operators, as detailed above, and US operators as well, generally with Stretched DC8s, who merged such charters with their substantial (at the time) military flights to Germany and the UK.
Britannia retreated to an all-737 fleet, but a few years later the experience was repeated when they started off on their 767 fleet, and they had to find alternative off-season work for large and expensive investments. The big Hadj charter programme moves forward by two weeks each year, so for several years it is useful for UK operators with a summer peak. Then as it moves back into that time the Canadian charter operators, who have a winter peak, come into contention for it.