No speculation......I'm happy to wait till the AAIB report.
I hate using LHR (operationally or as a passenger) for so many reasons........but there is no doubting the professionalism of all the emergency services, and of course the ATC'ers who, I have no doubt, did a fantastic job yesterday given the incident itself, and the immediate high workload in managing the diversions. Well done to all.
Regardless of the cause, it could so easily have been so much worse.