jabird - what do you mean by double taxation in this instance ?
Two doses of APD - one on outbound, the other on in. Compared to, say, a flight to cont. Europe, where there is only one dose of APD on the way out, and if taxed at all on the return, it is at a much lower rate.
Unlike, say, MAN or LBA, there is no option for business passengers to take the train to London from Belfast and be back home in time for tea!