from wikipedia

although John Camden Hotten in his 1859 Dictionary of Modern Slang, Cant and Vulgar Words states that (English) rhyming slang originated in the 1840s with 'chaunters' and 'patterers' (each a kind of travelling salesman; chaunters sold sheet music and patterers sold cheap tawdry goods at fairs and markets up and down the country) in the Seven Dials area of Westminster.[4][5]