I know that historically this was not possible, but I believe I’ve read on here that it now is.

I’m flying MCT-LHR-ARN with a nearly 6-hour layover at LHR. A friend is flying ORD-LHR-ARN with a 7-hour layover, and is flying in on AA so will be arriving at T3.

Can she re-clear security at T3, and can I take the flight connections bus and re-clear security at T3, so we can kill some of our time in the CX and QF lounges before making our way back to T5?