Now there was an airline, British Caledonian. Not the same or anywhere near to the situation in the 80’s when BA took over BCal. Firstly, BR operated out of LGW and nothing from LHR, wheras BA had a few routes from LGW which it was forced to operate from. Can ‘t remember why might have been something to do with making LGW more of a scheduled airport rather than one known for holiday charters.
There was duplication on domestic routes (MAN,GLA,EDI) and AMS and PAR but of course from LGW. BR was a much bigger airline than BMI is or has ever been and had a number of African and US routes.