I don't understand. What rules, laws or legislation requires this? The rules on board have always been in the realm of the operating carrier. US airlines don't allow anyone to congregate or queue for the bathrooms, certain Middle Eastern countries are bone dry. But BA don't align with either of these rules flying to the US or the ME. Surely the rules should simply be to don the mask at top of descent into the area which requires one on disembarking. Likewise a US-UK flight would allow masks off once seat belt signs are extinguished in the climb out. The notion that a carrier registered in England operating a British aeroplane under CAA regulations needs to have US FAA health mandates on British citizens over British airspace is an interesting one.

Can anyone quote me the relevant US or other legislation BA are being wary of here?