Parliament of the United Kingdom
The monarch (now King Charles III) is the sovereign in a constitutional monarchy and, theoretically, is the fount of all power in the United Kingdom. Bills must receive the Royal Assent before becoming Acts of Parliament and the monarch is responsible for summoning, proroguing and dissolving Parliament, normally upon the advice of the incumbent Prime Minister. It is now very rare for a monarch to object, but the sovereign still retains this prerogative for use if necessary.