Hawarden used to have a flight to Liverpool by British Eagle 1 -11 ... it took about 6 minutes and cost 10 /-. I think it dropped in on the way to/from Heathrow or Gatwick.
You could add Biggin to the list. What are the criteria for "could facilitate scheduled air services but at the moment do not." capable of taking a 737 or a BN-2 ?