Quite a few UK airports have stations and as a country i don tthink we can be criticised too much other than Heathrow Express which should have gone to Reading which is probably the best connected station other than Birmingham in the whole country., All the London airports have rail you include Luton and the Stansted one is not great because it is quite slow, Southampton and Southend have stations but are not exactly major airline hubs, nor is Teesside /Durham which has a station but no airlines. No UK airport has a proper mainline station like CDG,AMS and FRA but LHR has both express and Underground making it very accessible from all across London
. The idea of having airports in coastal locations would pretty much fall down at a glance. In UK coastal locations are:-
1 Not necessarily flat , especially in the west,
2 very windy and not necesarily in the direction where you can get 5-6 Kms of flat open space
3 Very popular with large seabirds
4 Foggy , esp in east and where not windy
5 Seldom close to rail links
Unlikely any Boris idea will come to fruition as we now know most of what he says is either a lie or impractical, Current back of envelope scheme seems to be Scotland -NI tunnel eventually being declared the next. pointless enterprise but a goldmine for consultants.in the meantime .