Smith what do you mean look at Darlington and Kent? Darlington is a town with in a county and Kent is a county, you can't compare the two. On top of that the centre of Darlington is about 5 miles to Durham Tees Valley (Teesside in old money). So there is already a service to both LHR and AMS for people to interline on. On top of that Darlington has a good train service into Kings Cross.