If neither have status then arrange to meet in a cafe or bar in T5.

Although best bet might be, if there's a few weeks before departure, both getting a SIM that works in the UK so if any problems occur they can contact each other. Won't cost more than a tenner (if anyone knows of prepaid SIMs with top ups less than £10 it'd be even better because in an emergency they'd likely still use less than £1 of credit).