The "Fourth Party" was a label given to a quartet of British MPs, Lord Randolph Churchill, Henry Drummond Wolff, John Gorst and Arthur Balfour, in the 1880-1885 parliament.
They attacked what they saw as the weakness of both the Liberal government and the Conservative opposition. Despite the label, they were all backbench members of the Conservative Party.
In the view of The New York Times, they would "act as skirmishers to the main body, popping out here and there to fire a shot at the Government and being ostensibly rebuked but really supported by the Conservative leaders."[1]
The later Conservative Party faction known as the Hughligans was "a self-conscious attempt to recreate the 'Fourth Party'", according to Rhodri Williams.[2]