HMRC must have worked out how much suspending APD on one leg of a return domestic flight in the UK would cost them and save airlines? Flybe rightly points out it penalises the regions (thought they would, it does), and yet probably simply because of the cost to the Treasury. I'd speculate it would be a gain overall? Think of the relative savings on LHR-LBA or LGW-NQY vs the train without £13 on one of the legs. Of course the carrier would absorb some of the saving but with significant coach/train competition (as exists on such routes) I suspect it makes a fairly compelling argument. Not to the Treasury, of course, but...