The loony left is a pejorative term used to describe those considered to be politically hard left. First recorded as used in 1977, the term was widely used in the United Kingdom in the campaign for the 1987 general election and subsequently both by the Conservative Party and by British newspapers that supported the party, as well as by more moderate factions within the Labour movement to refer to the activities of more militantly left-wing politicians that they believed moderate voters would perceive as extreme or unreasonable.

The label was directed at the policies and actions of some Labour-led inner-city councils and some Labour Party politicians. Although the labels hard left and soft left reflected a genuine political division within the Labour Party, loony left was by far the more often used label than either. While academics have depicted the era as of the "new urban left" (such as the rate-capping rebellion) as a throwback to earlier municipal militancy (e.g. Poplarism), wider media coverage tended to focus on the personalities of city leaders such as the Greater London Council's Ken Livingstone and Liverpool's Derek Hatton.