Originally Posted by
corporate-wage-slave
You can't just leave T5 and enter T3 like that, a T5 boarding pass won't get entry to T3 via landside. You have to use the transits to T5C, come back to T5A, go airside to T3, clear security, return via airside transfar, renegotiate your Ready to Fly Status, hope you keep your seats in the process and then reclear security. Mostly you would be mad to do this, when there are many easier options open to you.
I left T5 once when we were advised of a three-hour delay – so I could go and speak to a colleague who was at terminal four working – only to discover that, when I came back, indeed I had lost my seat as the system (and therefore the behind-the-scenes staff) thought I had changed my mind and did not want to fly. It was all a bit of a nightmare and not something I would ever contemplate again.