Final answer:
The UK is a constitutional monarchy with a parliamentary system where the monarch has ceremonial roles and the elected Parliament, led by the Prime Minister, wields political power.
Step-by-step explanation:
The United Kingdom's form of government is best described as a constitutional monarchy with a parliamentary system. The monarchy is largely ceremonial, with the reigning monarch acting as the head of state but with limited political power.
After considerable historical evolution, including the Glorious Revolution and the 1689 Bill of Rights, the UK has established a system where political authority and the ability to create policy lie with the democratically elected Parliament, led by the Prime Minister. Despite the monarch's reduced role in legislative affairs, the institution persists due to its traditional significance and the ceremonial and pageantry roles it fulfills, providing continuity and a sense of national identity.