During the Napoleonic Wars, the British Army used the term 'chosen man' to describe what would now be termed a Lance Corporal, the lowest rank of non-commissioned officer. Such a chosen man was, quite literally, the most exemplary private in a small group and chosen with special duties. In the case of William Surtees, he was chosen due to his fine marksmanship skills and quick learning abilities. As a chosen man he had been breveted with the duties of a recruiting corporal, and was soon afterwards promoted to the rank of corporal. The position of chosen man was accompanied by an additional 1p/day increase in pay from an ordinary private, the same given to the eventual rank of Lance Corporal, and a similar single rank chevron.

I attempted to look into Queens Regulations to find some more detail, but it was surprisingly sparse; perhaps further posters will be able to follow this up, especially in regard to when the switch to the more formal term of Lance Corporal occurred.

(I will admit, though I did get the inspiration for this response from the Sharpe series, as many might, I did find a primary source to back it up. - "Twenty-Five Years in the Rifle Brigade" by William Surtees, specifically pgs. 42 & 43)