In 2005, 118,000 people drove from our catchment area to MAN and NCL in order to fly to London, about half of them to onward connect. About 100,000 take the train to London. More by car and coach.
But isn't the problem that those who drive to MAN or NCL have the choice of going to LHR, LGW, STN, LCY and SOU from there? A service from Carlisle would only be able to serve one of these markets and thus limit the number of connections (particularly as a LHR would not be possible). The most attractive route for business people (LCY) would be rather useless for leisure pax and vice versa. In the end, a lot of people would still be driving to MAN and NCL despite a LON service from Carlisle.