FlyerTalk Forums Expert How-Tos and Guides
 

BA current newsflash here / London Cancellation list for Tuesday here
Rebooking policy for operating flights on Monday and Tuesday here / EC261 main thread here
ba.com/helpme one stop shop on BA.com giving lots of advice and pointers to where to claim expenses.
For EC261, delay/cancellation compensation is not payable for this event but BA is still liable for the Regulation's “Right to care” provisions. Refreshments can be claimed after 2 hours of delay departing (3 hours for flights longer than LHR-Rome, 4 hours for longhaul), £200 guideline for hotels - OK to book your own and charge back. £50 guideline for taxis. Meals, drinks and communication costs are also covered. Keep / photo receipts. If on a Buy on Board aircraft, use Avios to buy items - it will be faster to refund. For missing baggage, it's OK to claim essential items, such as clothing, toiletries. Keep / photo the receipts.