Originally Posted by GUWonder

At LHR for VS/DL flights, it's not the UK requiring this. For those flights from the UK to the US, it's the US Government's doing. So if this situation is one that hits and you want those responsible for it to look into a complaint about this: contact the US Government and the operating carrier, as the UK isn't in the prime positions to address a passenger complaint about this on flights from the UK to the US on DL/VS.