The prime minister of the United Kingdom is the head of government of the United Kingdom. The prime minister advises the sovereign on the exercise of much of the royal prerogative, chairs the Cabinet and selects its ministers. As modern prime ministers hold office by virtue of their ability to command the confidence of the House of Commons, they sit as members of Parliament. The office of prime minister is not established by any statute or constitutional document, but exists only by long-established convention, whereby the reigning monarch appoints as prime minister the person most likely to command the confidence of the House of Commons; this individual is typically the leader of the political party or coalition of parties that holds the largest number of seats in that chamber. The prime minister is ex officio also First Lord of the Treasury, Minister for the Civil Service and the minister responsible for national security. Indeed, certain privileges, such as residency of 10 Downing Street, are accorded to prime ministers by virtue of their position as First Lord of the Treasury. In 2019, the office of Minister for the Union was established; Boris Johnson became the first prime minister to hold this title. Rishi Sunak has been the incumbent prime minister since 25 October 2022. History The position of prime minister was not created; it evolved slowly and organically over three hundred years due to numerous Acts of Parliament, political developments, and accidents of history. The office is therefore best understood from a historical perspective. The origins of the position are found in constitutional changes that occurred during the Revolutionary Settlement (1688–1720) and the resulting shift of political power from the sovereign to Parliament. Although the sovereign was not stripped of their ancient prerogative powers and legally remained the head of government, politically it gradually became necessary for him or her to govern through a prime minister who could command a majority in Parliament. By the 1830s, the Westminster system of government (or cabinet government) had emerged; the prime minister had become primus inter pares or the first among equals in the Cabinet and the head of government in the United Kingdom. The political position of prime minister was enhanced by the development of modern political parties, the introduction of mass communication and photography. By the start of the 20th century the modern premiership had emerged; the office had become the pre-eminent