interliners?
the sixties were BKS days, it may be hard to believe but the Heathrow service was almost hourly, with 12 or more on weekdays!
We had Metropolitan, Genair and Capital operating sheds on the Gatwick. In fact Genair routed MME-LBA-LGW for some of the time. My recollection was that the services were well supported, so well so that weight and hold restrictions often became a problem.
As with Heathrow, most pax were interliners, my guess would be 90% minimum. So competition, wasnt with the railways as previous posters have suggested, as pax were using the service for onward travel around the globe. The main problem for the operators was not the lack of pax, but low revenues, because they only got a small share of the through fare to Timbuktu etc.
It seems strange that as BMI has greatly expanded their Heathrow services in recent years, (ie they can now feed more pax from LBA onto their onward flights), they decide to stop the service. However two things have operated to the detriment of the service. Firstly, the astounding growth at that airstrip on the wrong side of the Pennines whose name escapes me, (although you do seem to pay a premium to fly from there--as opposed to LHR/LGW). And secondly, there has even been some growth at LBA, making it easier to get around Europe and interline at more places.
But the demise of the CPH service is doubly bad news, (it had few pax in the Air UK days). I remember using the Brown Air Gulfstream 1 to FRA via HUYie, (also not well supported then), but hopefully, as suggested earlier, this may be a new destination for BM. It may seem to be logical, to their main hub, but why start another feeder service, having just dropped one to a major hub, in this economic climate and with slots hard to come by.... I wouldnt bank on it at all!