To get back to the terminal after arrival, you will need to go through security checkpoint, at least in my experience in LHR.
You maybe able to get back to sterile area of the terminal if you convince security check that you have connection, but it's not guaranteed (few weeks ago I had no problem going through connection security at T3 without showing boarding pass or printout, but I also saw other people stopped at checkpoint without itinerary). Even if you get to the terminal, you can be denied access to clobhouse without connecting flight.
The real question is why even try????
What's wrong with Revivals Lounge for a quick shower and breakfast before heading to town?
Last edited by AntonS; Aug 3, 2018 at 1:25 am