A parliamentary system of government similar to that used in Britain, variations of which are active in many of its former colonies. The model's key features are:
- The formal supremacy of a monarch -- "the Crown" -- over democratically elected representatives. In practice, the Crown or its representative acts only with the advice and consent of those representatives.
- Bicamerality -- the inclusion of two representative houses of government, such as a House of Commons and a House of Lords or Senate. Frequently but not invariably, members of one house are elected and members of the other are somehow appointed by the Crown.
- Partisan divisions within the houses, whereby the party winning the most elected seats "forms a government" at the invitation of the Crown, assuming control of the executive branch for as long as its leader, who normally becomes the prime minister commands enough votes to pass important legislation.
- Fusion of the executive and legislative branches -- government ministers are drawn from the ranks of the elected.
Within those broad rules are many variations that lead to slightly different balances of power and political cultures among countries that use the Westminster model. In Britain, for example, governments are more or less stuck with the reigning king or queen, who can influence public affairs -- gently and indirectly -- with little fear of being replaced by an irked prime minister. In the former colonies, however, the British monarch usually appoints a governor-general for a fixed term of a few years and only on the advice of the local sitting prime minister. That prime minister need fear no criticism, however, subdued, from someone who's normally appointed for long service to the PM or his or her party, and therefore actually has a sliver more authority in his or her country than the British prime minister has in Britain.
In Britain and Canada, vacancies in those countries' upper houses of Parliament are filled by appointment of the governing party; lords and senators in those countries exercise only about as much authority over public policy as they can pull together by the force of their arguments. In Australia, members of the Senate are elected and can claim popular support, so they get considerably more say in affairs of state.
In many of Britain's former colonies there's a periodic public discussion of shedding the British monarchy and instituting a republic, with a president being elected (possibly by popular vote, possibly by the members of Parliament) to take over the duties currently carried out by a governor-general. The rationale, of course, is that it's silly for a modern democracy to be ruled, even if it's only nominally, by a hereditary king or queen who lives in London, an ocean or two away. Setting aside the merits of self-rule versus hewing to tradition, prime ministers -- who call the shots -- generally don't like the idea of adding a new power centre, however trifling, to a system that's already gotten them put in charge.