The sound comes from a 2012 viral video of Muhammad Shahid Nazir, a fish trader at Queen's Market in east London, singing his sales patter to attract customers to his one-pound fish stall. Filmed by a passer-by and shared on YouTube, the catchy chant was remixed, covered and shared millions of times, turning the trader into an internet celebrity and leading to a recorded version of the song. It endures online because the tune is simple, cheerful and instantly tied to bargain hunting, making it a shorthand for anything cheap and good value.