I remember discussion about this sort of thing years ago. Being in the UK for one night that included midnight local time constituted one working day in the UK, this was changed/they wanted to change(?) to, If you arrive one day and leave the next that is two working days etc. Not sure if that ever became the new tax law or not? 20 working days in UK for a ME based airline would not be hard to achieve, I would think, a lot less likely if based in the Far East/SE Asia.
As I read the document, one of the much stricter proposed rules relates to
the issue of availability of accomodation on visits to UK, as another poster has
rightly pointed out. The guys and gals who really need to seek advice from
reliable sources about this are the commuters whose families reside permanently
in UK.
A court case a few years ago really hammered a man who was based for work in France but had all his family in England, he got caught for thousands of £s back tax but I think he may have complicated the issue by lying to HMRC. Bit of a red herring but didn't Cathay Pacific change the status of it's overseas based pilots by making them 'On-Shore' in their base country?