The only reasonable London area destination is Heathrow, for connections onto other carriers, to supplement the point-to-point traffic to the stage that such flights become worthwhile. And we all know how Heathrow slots for domestic flights have been whittled away to use them for more profitable intercontinental flights.
It is a significant issue for the UK regions that this connectivity has been lost. The only hope on the horizon is that, if the third runway at Heathrow is finally approved, a proportion of the additional slots that become availabe are ring-fenced for UK domestic services to Leeds, Inverness, Liverpool, etc.
It would surely get the support of many regional MPs to have their connections back. MPs in any event are very substanial users of domestic flights themselves.
The long-standing story that domestic flights are "unprofitable" is entirely dependent on the way that through fare revenue is attributed. If it becomes feasible for passengers to route Leeds-London-Los Angeles on BA instead of Leeds-Amsterdam-Los Angeles on KLM, BA will be supportive, even if they had to get FlyBe to paint up some Dash 8s in BA colours. Point-to-point in its own right (such as the Easy service from Liverpool to Luton), or just connecting in its own right (such as the KLM Liverpool to Amsterdam) are often not worthwhile, and so both have been lost. Put both traffics together on one aircraft and things change.