My badge arrived from Poppy Shop this morning , these were only on their site for a very short time and are no longer available (not even showing as 'out of stock').
The Battle of Britain was from July - October 1940 and the 15th September 1940 was officially named Battle of Britain Day as it was the day when RAF Fighter Command claimed what proved to be a decisive victory over the German Luftwaffe.
Hopefully Poppy Shop will get more of these badges before the anniversary but as they had supply/delivery problems with VE Day 75 items I'm just glad I ordered mine as soon as they appeared.