Not Going Out (2006)

S15E6 Banksy

Lee stumbles upon a previously unknown Banksy piece and, in a reckless bid for recognition and riches, tries to make off with it. But when a security guard catches him in the act, he panics and lets slip a suggestion that he himself might be Banksy, hoping to slip free. That one desperate lie backfires spectacularly—suddenly, he's trapped in the middle of a blackmail scheme.