According to local folklore, the term originates from an apocryphal incident in which a monkey was hanged in the town of Hartlepool, England. During the Napoleonic Wars, a French chasse-marée was wrecked in a storm off the coast of Hartlepool. The only survivor from the ship was a monkey, allegedly dressed in a French Army uniform to provide amusement for the crew. On finding the monkey on the beach, a group of locals decided to hold an impromptu trial. Because the monkey was unable to answer their questions, and because they had seen neither a monkey nor a Frenchman before, they concluded that the monkey must be a French spy.[2] Being found guilty, the animal was duly sentenced to death and summarily hanged on the beach.

Similarly, they call people from South Shields (nearby town) Sand Dancers for not fully understood reasons:

https://www.thenorthernecho.co.uk/news/crime/20201881.reasons-south-shields-people-called-sand-dancers/