Over the past 2 days there is an odd coincidence of B767-300 diversions going to London.
AAL 174 Feb 28 KRDU-EGLL goes over Bangor Maine then diverts to KORD
AAL 90 Feb 28 KORD-EGLL goes back over Toronto and returns to KORD
UAL 922 Feb 27 KIAD-EGLL goes past Long Island and returns to KIAD
They look like they may also have been mechanical rather than medical diversions. The 2 AAL aircraft went to ORD and the UAL to IAD. These airlines have hubs at the airports they diverted to.