Ok, did a little research, but firstly wish to thank
https://asahelena.wixsite.com/ for their contribution to the button community.
What information I was able to gather was that this backmark dates no earlier than 1810 and probably no later than 1820. Now clearly I have a vested interest in this as I believe the cut of my coat and collar dates it to pre 1812, but I defer to some of you experts here.
Here are the images with that back mark that I was able to pull off their site. Many of their dates are off so I had to go by experience as digger of buttons myself
Interestingly, the Berkshire Militia has the I Nutting Covent Garden which is a confirmed pre 1814 button and also displayed here with the C. Jennings with plume