Prime Minister of the United Kingdom in the context of "Parliament of the United Kingdom"

The constitution of the United Kingdom comprises the written and unwritten arrangements that establish the United Kingdom of Great Britain and Northern Ireland as a political body. Unlike in most countries, no official attempt has been made to codify such arrangements into a single document, thus it is known as an uncodified constitution. This enables the constitution to be easily changed as no provisions are formally entrenched.

The Supreme Court of the United Kingdom and its predecessor, the Appellate Committee of the House of Lords, have recognised and affirmed constitutional principles such as parliamentary sovereignty, the rule of law, democracy, and upholding international law. It also recognises that some Acts of Parliament have special constitutional status. These include the Magna Carta, which in 1215 required the King to call a "common counsel" (now called Parliament) to represent the people, to hold courts in a fixed place, to guarantee fair trials, to guarantee free movement of people, to free the church from the state, and to guarantee rights of "common" people to use the land. After the Glorious Revolution, the Bill of Rights 1689 and the Claim of Right Act 1689 cemented Parliament's position as the supreme law-making body, and said that the "election of members of Parliament ought to be free". The Treaty of Union in 1706 and the Acts of Union 1707 united the Kingdoms of England, Wales and Scotland, the Acts of Union 1800 joined Ireland, but the Irish Free State separated after the Anglo-Irish Treaty in 1922, leaving Northern Ireland within the UK. After struggles for universal suffrage, the UK guaranteed every adult citizen over 21 years the equal right to vote in the Representation of the People (Equal Franchise) Act 1928. After World War II, the UK became a founding member of the Council of Europe to uphold human rights, and the United Nations to guarantee international peace and security. The UK was a member of the European Union, joining its predecessor in 1973, but left in 2020. The UK is also a founding member of the International Labour Organization and the World Trade Organization to participate in regulating the global economy.

The Brexit withdrawal agreement, officially titled Agreement on the withdrawal of the United Kingdom of Great Britain and Northern Ireland from the European Union and the European Atomic Energy Community, is a treaty between the European Union (EU), Euratom, and the United Kingdom (UK), signed on 24 January 2020, setting the terms of the withdrawal of the UK from the EU and Euratom. The text of the treaty was published on 17 October 2019, and is a renegotiated version of an agreement published in November 2018. The earlier version of the withdrawal agreement was rejected by the House of Commons on three occasions, leading to the resignation of Theresa May as Prime Minister and the appointment of Boris Johnson as the new prime minister on 24 July 2019.

The Parliament of the United Kingdom gave its approval to the agreement on 23 January 2020 and the UK government deposited Britain's instrument of ratification on 29 January 2020. The agreement was ratified by the Council of the European Union on 30 January 2020, following the consent of the European Parliament on 29 January 2020. The United Kingdom's withdrawal from the Union took effect on 11 p.m. GMT on 31 January 2020, and at that moment the Withdrawal Agreement entered into force, as per its article 185.

Diplomacy is the communication by representatives of state, intergovernmental, or non-governmental institutions intended to influence events in the international system.

Diplomacy is the main instrument of foreign policy which represents the broader goals and strategies that guide a state's interactions with the rest of the world. International treaties, agreements, alliances, and other manifestations of international relations are usually the result of diplomatic negotiations and processes. Diplomats may also help shape a state by advising government officials.

The House of Commons is the lower house of the Parliament of the United Kingdom. Like the upper house, the House of Lords, it meets in the Palace of Westminster in London, England. The House of Commons is an elected body consisting of 650 members known as members of Parliament (MPs), who are elected to represent constituencies by the first-past-the-post system and hold their seats until Parliament is dissolved.

The House of Commons of England began to evolve in the 13th and 14th centuries. In 1707 it became the House of Commons of Great Britain after the political union with Scotland, and from 1801 it also became the House of Commons for Ireland after the political union of Great Britain and Ireland. In 1922, the body became the House of Commons of the United Kingdom of Great Britain and Northern Ireland after the independence of the Irish Free State. Under the Parliament Acts 1911 and 1949, the Lords' power to reject legislation was reduced to a delaying power. The government is solely responsible to the House of Commons and the prime minister stays in office only as long as they retain the confidence of a majority of the Commons.

The monarchy of the United Kingdom, commonly referred to as the British monarchy, is the form of government used by the United Kingdom by which a hereditary monarch reigns as the head of state, with their powers regulated by the British constitution. The term may also refer to the role of the royal family within the UK's broader political structure. The monarch since 8 September 2022 is King Charles III, who ascended the throne on the death of Queen Elizabeth II, his mother.

The monarch and their immediate family undertake various official, ceremonial, diplomatic and representational duties. Although formally the monarch has authority over the government—which is known as "His/Her Majesty's Government"—this power may only be used according to laws enacted in Parliament and within constraints of convention and precedent. In practice the monarch's role, including that of Head of the Armed Forces, is limited to functions such as bestowing honours and appointing the prime minister, which are performed in a non-partisan manner. The UK Government has called the monarchy "a unique soft power and diplomatic asset". The Crown also occupies a unique cultural role, serving as an unofficial brand ambassador for British interests and values abroad, increasing tourism at home, and promoting charities throughout civil society.