Cymro

Also while ex-INV is always about lower departure taxes, the fares are often lower than elsewhere in the UK - presumably to attract ex-EU type custom as well.

(NB flying out of the EU really is not about lower departure taxes, though it plays a role. The main reason is that, if you want to fly AMS-BKK you would do so non-stop on KLM, all things being equal. To make sure that all things are not equal, BA offers prices that are much lower out of AMS than it does out of LHR to give Dutch people an incentive to change at Heathrow. However, fortunately for us, LHR-AMS is only a short hop and a very easy turnaround, which justifies the price saving over a non-stop flight. The same applies to lots of other routes starting all over Europe.