European regulations on delayed / cancelled flights MAY happen, depending on whether the accident at LHR (If they invoke it) can be considered as Force Majeure. This being said, airlines ALWAYS claim that these texts do not apply and finally relent when you insist and theraten to become noisy. It has happened to me several times and they ALWAYS cough up, ALWAYS claiming that they are not responsible but do it as a gesture of good will.

To know your rights more precisely, go to the BA page on European regulations, there is a link, or try
http://observer.guardian.co.uk/cash/story/0,,1853923,00.html

Good luck