To add to what Lester says, the manuscript is from the Bosham Band. Bosham (prounounced Boz-um) is a beautiful village on (and frequently under) Chichester Harbour at the exreme west end of Sussex. As far as I know, it appears there simply as Cotillion. It isn't in 'The Sussex Tunebook' but was published (probably for the first time in 200 years in 'Lewes Favourites' which is also sadly now out of print but the tunes from it are available in various forms here Lewes Favourites. The Cotillion is first in the book. It is graatifying to see how it has spread.
The four part arrangement on the video is by Stuart Walker our musical director who, as Valmai has said, had to stand down this year. The serpent's bass line is very much his own as he didn't have the range for the written one. Valmai has also written a three part arrangement. She is setting to the serpent player's left playing concertina.