Originally Posted by Dave Noble

I cannot see how EC261 does not apply assuming that the passenger did fly the outbound journey as ticketed

That the airline chose to cancel the persons booking would then make the airline liable for EC261 compensation

If the passenger didn't fly the outbound , then the airline would be justified in not permitting the return travel

If the person travelling was not arriving on an EU passport into London, the passenger will have a stamp in passport showing arrival into London on that day - not sure if it shows terminal or not