Hi: Ony 3 hallmarks with a duty mark seems to go against convention. The manufacturers mark closely resembles London manufacturers Francis Butty & Nich Dumee (18th century) a square stamp with letters in each quadrant. The duty, date & lion passat seem most similar to that from London 1810-1811 but no leopards head. Anyone? Not sure if pic's were attached, I tried my best. Thanks !!
It's usual for teaspoons of this period to have such hallmarks. From the pictures you sent me I can see that it is 1810, but I can't make out the makers' mark.