Thank you very much, SpeedbirdLHR - useful and informative.

I assure you that the lack of information was not confined to T4. Exercising privilege I probably shouldn't have, I called the EC gold line at about 1210 to enquire what would happen now that the flight was cancelled. The very polite and helpful lady checked her systems and saw only the delay information (to 1400) at that time. Of course, I told her what ba.com was showing. She went and checked and a few minutes later told me that my wife would be rebooked on the next BA flight.

I left out one piece of information in an effort not to take up too much space. My wife doesn't (yet) have access to BA lounges when travelling alone, so she used the Holideck lounge close to Gate 15 until the time she had to go to the gate. From that point on, there was no information at the gate. She called me just after 1145, the nominal departure time. I told her the flight had been delayed - first 2 1/4 hours, then (a few minutes later) 2 1/2 hours, then cancelled.

It would certainly be useful to know what information was available to passengers and if she somehow missed it. When changing her BP, she asked the reason and was told snow in Zurich. We don't know whether that was an informed or a speculative response. Clearly, it didn't apply to other BA or LX planes on that route, and as noted before BA's other LHR services ran very close to time. Whatever the problem, it seems specific to that plane and/or crew.

The delay on the later plane was engineering-based and passengers onboard were kept informed.

One more thing. I'd always assumed that FF credit was triggered at departure, i.e. when the flight flown had closed or later. That must be wrong as the originally booked flight 714 shows in her EC account rather than the substituted 716.