Derrick's partner, Joy, dances with the knots. As Valmai says, he plays, with Joy Lewis, Ian Chisholm, Will Duke and Sue Evans in the Twagger Band.
Derrick and Joy go out as a duo - very popular in Sussex - and Derrick is also a regular at the monthly session in the Bull at Ditchling.

If you look at the opening credits of the 1930s version of "The Scarlet Pimpernel" with Lesley Howard, you'll see a marching band led by a serpent player. Its origins are in Italy and/or France.