I did have London Fields down as we were so close, so e-mailed them to check if they would be open, and they were kind enough to reply, but sadly they won't be open that Sunday.
Added 9.11.12. We get to Chertsey on Wednesday, and have checked on here for pubs in the walkable area. As well as the 2 Good Beer Guide pubs we know - Coach and Horses and Thyme at the Tavern - I have a few more. Kingfisher, Boathouse, Crown, (Youngs we did in August), Castle, Prince Regent, King's Head, George, Ghurka Lounge, and Swan.
Does anyone have any gen on these that may be useful. Lots of ancient reviews around.