I decided to take a look at the Oasis Hong Kong Airlines website, and stuck in some random dates in Dec/Jan to look at the fares. The basic (economy) fare each way for the dates I've picked is £265. Taxes/charges on the HKG-LGW leg are £44.38, but on the LGW-HKG leg they're a rather steep £106.67. So I hover over the tax amount to get a breakdown, and discover to my chagrin that they are charging the UK Govt's £20 economy class APD
AND the £40 business class APD on the economy fare!
I'm sure this is cock-up rather than conspiracy (the APD charge for the business class fare is correct) but it's a bit unfortunate. The airline is not only scaring away potential passengers by pricing £40 higher than it actually planned to do, but it's also opening the door to a lot of customer unhappiness when people realise that they've been overcharged - at the very least there'll be a major administrative task to refund all the wrongly-collected APD to people's credit cards. Hope it gets fixed soon (and yes, I've emailed their info address to flag this up).
(PS: as of 18 Oct it was fixed.)