The LGW 777's are being refurbished from early next year and this is the new layout which shows the paired seating at the back of the plane.
So, it looks like your flight is planned for that at the moment although your seatmap shows 9 across?!
Welcome to Flyertalk and the BA Board
Wintle1970 and thanks for your question. There is more info on this, way too much to list here and many other matters which you may find useful.
Pete
BA 777 Seating Guide