What type of monarchy is the United Kingdom?
A constitutional monarchy is a form of monarchy in which the sovereign exercises authority in accordance with a written or unwritten constitution, while the Legislative Power is exercised by a Parliament, usually elected by citizens.
In the Kingdom of England, the Glorious Revolution of 1688 led to a constitutional monarchy restricted by laws such as the Bill of Rights 1689 and the Act of Settlement 1701, although limits on the power of the monarch ("a limited monarchy") are much older than that (see Magna Carta). At the same time, in Scotland, the Convention of Estates enacted the Claim of Right Act 1689, which placed similar limits on the Scottish monarchy.
Today, the role of the British monarch is by convention effectively ceremonial. Instead, the British Parliament and the Government – chiefly in the office of Prime Minister of the United Kingdom – exercise their powers under "Royal (or Crown) Prerogative": on behalf of the monarch and through powers still formally possessed by the Monarch.
No person may accept significant public office without swearing an oath of allegiance to the Queen. With few exceptions, the monarch is bound by constitutional convention to act on the advice of the Government.