Originally Posted by LondonElite

No airline plays loosy-goosy with entry requirements, and certainly not now. As always, it is the traveller's responsibility to check whether they are able to travel and be admitted on the day of travel with correct paperwork, etc. This is independent of when the ticket was bought. It is not BA's fault that entry rules are what they are.

I understand the OP's motivation, and I sympathise and appreciate that to most rational people, staying airside is, for the practical purpose of the entry regulation, the same as being in transit. But the fact is that it is not, and that's not BA's fault.