I did a turnaround on MRU but on LHR-MRU-LHR.

Two ladies from the BA-office were waiting for me just outside the plane, and they escorted me directly to the BA-lounge, where my passport was checked by someone of immigraton (a bit strange as I was in transit).
Then they gave me my XONEX-ticket and took a print of my CC-card.
After I signed the CC-bill, one of the ladies went out of the lounge to pick up my Boarding pass, and they even escorted me back to the Gate at departure time.

So The ba-people in MRU are really great and give you a really good service, and they're getting used to see some crazy turnaround people