I never heard about the special reduction (I'll have to read into it), anyhow I checked the ADP thing on HMRC, and then checked it against WebFlyer Mile Calculator and it's well within the 2001-4000 mile thing, I think it's really quite insane, I checked Halifax from LHR and it appears not to be exempt from the excessive ADP.
Yeah sorry Dontgothere, I guess my post was a bit poorly worded. As some of the others have more successfully written, I meant the long haul flights out of Belfast being at a reduced rate of APD. I mentioned measurements being taken from London because I heard recently that it is a stumbling block for a turkey flight not getting the reduced APD (would quailfy from BFS but the HMRC measurements are taken from London - I do tend to get info about 3rd hand so sorry if it takes anyone in the wrong direction)