If your flight has the new Club World cabin there should be a reasonable selection of sandwiches, cold and hot snacks in the "Club Kitchen" that you can have any time after the seatbelt lights have gone off.
http://www.britishairways.com/travel...n/public/en_gb

If it doesn't have the new cabin I think there should still be sandwiches / cold snacks available for you to eat when you want but not hot snacks.