Hi! Have you thought about having tea instead of a full meal? Some years ago, we had a big family gathering and wanted to do something fancy, so we had afternoon tea at the Savoy. It's not pub grub and isn't cheap-cheap, but it's less than a full meal, and they just kept bringing food --sandwiches, tea, more sandwiches, sumptuous desserts -- and we obliged by eating it until we could barely move.
If you want to just go someplace cool for a bite and don't mind self-service, try the crypt under St Martin's in the Fields on Trafalgar Square. In the evening, there are usually candles, you can move little tables together to make a bigger one, they serve wine as well as a variety of soft drinks, the food selection is really good --and it's pretty cheap. There are wonderful concerts there, as well. Check it out on the Web :
http://www.stmartin-in-the-fields.org/jserv/home/index.jsp Happy Holidays!!
St. James Picadilly is another old church with great ambiance, music and food. xo Katelyn