OK, so I'm in the FIRST lounge at T1 with boarding pass in my grubby mitt. Thanks to OLCI I snagged 4C on BA 676 so hopefully I should be at the front of the immigration queue to buy my visa / get into Turkey, giving me maximum time to pick up my ticket + check in to get back here in about 9 hours. Full report from LHR on my return (today if it works, tomorrow if not...)

Wish me luck!

CT