Heathrow: Air France and Luxair certainly. Possibly TAP and Tunis Air
Also, and in my case definitely: Finnair, SAS, Iberia, Austrian, Swissair, Alitalia, Royal Air Maroc, Sabena, JAT ....
My first flights aboard a Caravelle were LHR-BCN and return during the summer of '69. Iberia obviously, who were kind enough to give me ID100 tickets (freebees!) - in those days, the only way to fly!
Then, from 1972 onwards, various flights on Caravelles within Brazil on Cruzeiro do Sul's domestic network. Great days. Lively nights.