The Baker Street Irregulars, also known as the Ministry of Ungentlemanly Warfare, was a covert organisation to which the Eleventh Doctor said Alec Palmer belonged. (TV: Hide)
Behind the scenes
Though not made explicit in Hide, both of these terms were codenames for the Special Operations Executive, a real world organisation that existed in Britain chiefly in World War II. It was called the "Baker Street Irregulars" after the name of the street on which the group's headquarters was located.