It was Hartlepool, (they elected a monkey as Mayor this year) but true, the original monkey was the pet of a French ships captain, shipwrecked during the Napoleonic wars and washed ashore. The monkey was dressed in a sailors costume and as it didn't speak English (and there were no French sailors left alive) the good residents of Hartlepool tried the monkey as a spy, found it guilty and hanged it.
I think there are some web sites about the story.