The Met man screwed up.
The forecast was for some really heavy showers. All crew got a message saying that ops were working on a de-icing rate of 12 per hour at LHR. This would have led to some serious delays. As de-icing at LHR is done on stand there would have been further knock on delays as aircraft waited for vacant stands at the terminal.
I think BA was for once being proactive and trying to get ahead of the game. All the crew turned up - the snow didn't.
As for compensation - we leave that to the bean counters in Waterworld.
T'bug