Skip the BA mainline JET base never got more than 6 - Yes 6 residents plus a few outstationed in Glasgow, Belfast and Edinburgh.Plus the upto two Trans Atlantic birds.
That's right, of the 18 BAC-111-510s delivered, I recall 6 based at MAN and the other 12 at Berlin, with all 18 cycling through MAN for maintenance. When the Berlin base ran down the 12 were scattered around other UK airports. A bunch of other 1-11s were added later, mainly as a result of mergers and take overs, but were based elsewhere (mainly BHX)
When the British Regional joined they added some of the ATPs and Jetstreams another 4 or five .
And who could ever forget BACON and their collection of Dash-8s and Embraers - which unfortunately turned out to be a bit of a pig as far as BA were concerned and ended in tears
Then there were the BAe146s, which arrived just as the Euro carriers were all upgrading at MAN to A320s and 737NGs.
Certainly no shortage of attempts over the years by BA with a multitude of aircraft types and brandings, but none of them came close to matching the scale of today's based carriers.