I frankly wouldn't recommend scheming the system in such a way and would personally consider it against my morals even though others can of course do anything they want and feel comfortable with and as long as they assume the risks however slim they may be.

If they have an 8 hour layover, some other lounges allow paid access, and there are also day rooms in and around Heathrow which are undoubtedly a far better use of time than waiting for 8 hours in a lounge in any case.