Incidentally it was the fact that the 1-11 had to operate via OST to many Channel Airways destinations that forced the move to STN. Quite why they bought that aircraft knowing its severe SEN limitations, rather than the B737 and DC9 that they also considered. remains a mystery.
At the time I recall it being stated officially that Jack Jones was keen to buy British.
There may have been an element of that but, after all, he had had a large fleet of DC-3s. More likely was the fact that BAC were desperate to sell their 1-11 and offered a financial package that was hard to refuse. Boeing, having already secured Britannia Airways, probably wouldn't match that. At the time I felt it was a big mistake but I guess the 737 was a noisy aircraft (though not quite as noisy as the 1-11 if memory serves me correctly) and Mr Budge and his Southend Jet Protest Association would have made intensive operations very difficult for the airport. Now that jets are SO much quieter there isn't the same level of opposition that there was back then.