Where I was, there was a fair bit of interaction and cross-fertilisation. Both airlines had a very similar 3-year General Apprenticeship scheme, with the BEA and BOAC groups (each 30-50 strong) being merged for the academic parts of the course at Ealing or Slough Techs, so a lot of close friendships were forged at that stage. I shared a flat with three BEA guys. Then there was the Salford Uni Transport Admin course which was jointly supported by the two airlines. In my year there were three BOAC and two BEA people.
Then in the seventies, round about merger time, there were quite a few of my ex BEA pals around Speedbird House or down the longhaul routes.