From Owen Jones’s The Establishment, Location 774. According to this biography of George Osborne, which I’m amazed at myself for having read, the window of political acceptability is a key factor in Osborne’s strategic thinking:
What the corporate-backed outriders have achieved is this. They have helped shift the goalposts of debate in Britain, making ideas that were once ludicrous, absurd and wacky become the new common sense. In the terminology of right-wing political thinkers, they have shifted the ‘Overton Window’. The Overton Window is a cherished concept of the US right, coined in homage to Joseph P. Overton, the late vice-president of the right-wing think tank the Mackinac Center for Public Policy. It describes what is seen as politically possible or reasonable at any given time while remaining within the political mainstream. But the very nature of outriders is that they can float ideas or policies that a politician would not dare mention. In doing so, they shift the Window.