This is not just a UK problem: here is the official view from ACI that represents the worlds airport operators:
https://twitter.com/askhelios/status/446595828040622080
The airline market is dynamic and changing fast, the impact of LCC, the Gulf carriers and both of rising taxes and rising fuel costs mean that airlines need to fly larger aircraft with lower seat mile costs. Smaller airports generally don't have the year round demand to support the larger aircraft, as has been said already.
This has been Flybe's market challenge, they have been unable to match the seat costs of competitors. So most potential pax travel to the nearest alternate airport with the airline offering lowest fares. In the UK that's rarely more than a two hour drive. This impacts not only Flybe but every other airline.
I expect that the next ten years will see more UK airports close but the pax traffic will continue to grow and consolidate elsewhere.
Conversely I also expect KLM in particular and Turkish, to seek out more regional airports in UK and elsewhere to serve, as a means of differentiating from and competing with the Gulf carriers. Market dynamics at work.
Interesting times as always!
FF