|Southampton Airport with the railway and terminal only 99 steps apart.|
it's a bit chicken and egg as operators don't want to fly to smaller airports because of lack of demand and passengers stop looking for any flights that go from regional airports because they assume there are no flights.
Skyscanner is very good as they do give you a pretty comprehensive view of what’s operating and what’s not, also they feature connecting flights which can allow you to travel locally but not necessarily directly,
Airports to look at that you may overlook, if you are in the South East then Southampton has it's own rail link and is only 61 minutes from Clapham Junction (67 Mins from waterloo) by a direct train also its on the junction of two motorways the M3 and the M27, Bournemouth is technically in the South West because it's in the county of Dorset, but it's only 30 minutes from Southampton by motorway or it has a railway station reasonably near at Christchurch.
Southend is a good alternative to Stansted if you live in Essex or East London and Luton has a rail link although the last last 500M is by a coach, but there has been for a while plans to build a light railway from Luton Parkway to the airport up the hill.
Manston (Kent International was closed down, but there are rumours of it opening up again, this would provide a valuable new Runway of over 3000M for the South East
In the West Country Bristol is king, but you have alternate airports in Exeter, Newquay, Bournemouth or even Cardiff.
The Midlands you have Birmingham and East Midlands, but Luton can always be an alternate.
In the Northwest, Blackpool was lost to operations, but the favorite is Manchester and there is of course Liverpool it's smaller rival. Leeds Bradford is a credible competitor and there is Doncaster (Sheffield) airport which could be for people from the North West, but also form the North east and Hull.
North East wise you have Hull (Humberside), Doncaster, Teeside and Newcastle airports.
Then you have Scotland with Glasgow Intl, Prestwick as an alternative or Edinburgh which is 30 miles away on the M8 motorway. There is a scheme in scotland where as Scot Rail will give 50% discounted tickets to Prestwick airport from anywhere in Scotland National rail link
Edinburgh does have Dundee also as a rival and you have Inverness in the north of Scotland
of course I have failed to mention one or two other airports, Norwich in East Anglia, Lydd airport in Kent, Gloucester and Cambridge airports, we need to cherish our local airports because the House developers are after them.