Scotland has devolved responsibilty for airports including APD and could abolish APD at PIK to increase passenger numbers, GLA/EDI might object but reducing APD might be a fairer way of supporting PIK than a subsidy paid for by all tax payers.
I'd like to see the legal advice on reducing APD at just one airport (which happened to be owned by the same body setting the tax level...). Don't follow the fairness point - isn't the general tax payer picking up the bill either way?