Isn't it possible to get a tax refund (subject to a fee of £15), even if you simply no-show?

Hence with LHR's substantial passenger charges (£23.18 currently for short haul European flights, reducing to "merely" £21.79 next year) and £13 in APD, you would in fact still get something back afterwards.

The fact that the passenger charges and APD are lower for domestic flights means there's actually an incentive to book somewhere else that's within the 650 mile band!