Published in 1808 by Wm. Miller, this Atkinson painting shows English troops drilling. You can see the antiquated three-rank firing by platoon in action. While still in the manual of the time, the three-rank technique was not used in favor of the two-rank technique.
A General seems to be observer the troops. He is the man on horseback, second from the left. We can tell he is of a high rank based on his uniform.
The regiment appears to be a buff-faced regiment. The facings and the crossbelt straps appear to the be the same color. It could be a militia unit, a closer look at the soldiers will have to be undertaken to determine the regiment.