From the BAA site
Flight cancellation update
Flights suspended until 07:00 tomorrow, Sunday 18 April
Last updated: 15:00 GMT, 17 April 2010
Following the latest advice from NATS, all flights to and from all BAA airports are suspended until 07:00 tomorrow at the earliest. Passengers due to fly today should not travel to these airports until further notice, and should remain in touch with their airlines.
We expect NATS to provide a further update around 21:00 today. We appreciate the continued patience of passengers at this difficult time and will provide updates as often as possible.