The United Kingdom is unusual in having no single written constitutional document that can be enforced by the courts. Instead it has a political constitution, which relies heavily on norms and conventions. When challenges arise, it rests on a shared understanding of the rules and the principal actors being willing, for the most part, to abide by them—the “good chaps” theory of government. When actors step out of line, or even contemplate doing so, the system of political checks and balances—involving MPs, members of the House of Lords, ministers, civil servants, the devolved institutions, the media and ultimately the public—is meant to ensure that they are either unable to or are punished for their behaviour.