Thanks as this is useful information. Just to double check, airlines have a duty of care AND should book you on the next available flight (not necessarily the next available BA flight?) I have to admit I'd have done exactly what the op did and I'd have expected BA to pay for my new flight without fuss.

If you are a family travelling you can face enormous costs when stranded like this. I find that you have to get ahead of the game and make decisions very quickly too as there are often only so many seats available on alternative flights.