The philosophical movement that dominated Oxford and Cambridge from roughly 1870 to 1920, drawing on Hegel and the German idealists to build a distinctively British account of ethics, metaphysics and the state.
Its political importance is larger than its philosophical reputation. T. H. Green argued that freedom worth the name is a positive capacity — the ability actually to do and become things — rather than the mere absence of interference, and that the state therefore has a duty to remove the obstacles of ignorance, illness and destitution that prevent people from exercising it. That argument, developed by his students and popularized through the New Liberalism, supplied much of the intellectual groundwork for the British welfare state; it is the direct ancestor of the positive-liberty tradition Berlin would later warn against.
Bradley and Bosanquet developed the metaphysics further and, in Bosanquet's case, a considerably more state-centered politics that critics including Hobhouse attacked during the First World War as an English apology for Prussian doctrine. Collingwood, the last major figure, turned to the philosophy of history and the logic of question and answer.
The movement was displaced with unusual speed. Moore and Russell's revolt around 1903 against idealist metaphysics is conventionally treated as the founding act of analytic philosophy, and British idealism went from orthodoxy to embarrassment within a generation. Its continuities are easy to miss: Oakeshott was trained in it and carried its conception of experience as modally distinct throughout his conservative political writing, and recent scholarship has been substantially concerned with showing that the analytic revolt misdescribed what it was overthrowing.