I suspect this concern is overblown. APD is for the vast majority of flights £13. The PSC at Edinburgh is £2 more than Newcastle, so even with zero APD, that makes the net saving £11 per person.

The area North of Newcastle is sparsely populated, so we'll discount that. Go south of the Tyne and you're looking at a drive in excess of 2 hrs to get to EDI. A family of 4 would struggle to recover the £22 saving on petrol costs. 4 adults might just about be able to make it work for the £44 saving, but you're adding hours to the trip.

Also worth noting that despite the APD waiver, UA have pulled their Belfast - NYC service.