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.

[9][10] The prime minister alongside the cabinet proposes new legislation and decide on key policies that fit their agenda which is then passed by an act of parliament.

Prime ministerial power itself evolved gradually alongside the office itself which have played an increasingly prominent role in British politics since the early 20th century.

[20] The position of prime minister was not created but evolved slowly and organically over three hundred years due to numerous Acts of Parliament, political developments, and accidents of history.

The Whigs supported parliamentary sovereignty and constitutional monarchy whilst the Tories favoured the divine right of kings and the deposed James II.

[28] The head of Treasury, as Lord Treasurer, was give the power in 1706 following Standing Order Number 66 to draft money bills (budgets) instead of MPs outside of government.

[39] His financial abilities in handling the repercussions in the aftermath of the South Sea Bubble[40] earned him the support of commercial and landed interests, pursued a largely peaceful foreign policy, lowered taxes and reduced national debt[41] while his skilful management of Commons affairs solidified his dominance in Parliament by operating as a "Screen-Master General", pulling strings and sullying favour whenever necessary.

[43] Despite being able to successfully hold power for 20 years, Walpole faced fierce opposition over alleged bribery and corruption in Parliament[44] and following a disastrous war with Spain,[45] he resigned in 1742 and was succeeded by the Earl of Wilmington.

Vernon Bogdanor argues that the abilities to declare war, negotiate treaties and deploy the armed forces have historically been part of the monarch's royal authority but have slowly evolved into a function of the office of prime minister.

Solely upon the advice of the prime minister, the sovereign exercises many statutory and prerogative powers, including high judicial, political, official and Church of England ecclesiastical appointments; the conferral of peerages and some knighthoods, decorations and other important honours.

[69] Bagehot points out that this power is based on the prime minister's ability to operate the "machinery of government" that allows them to guide legislation that align with their party's political and ideological priorities.

Bogdanor states that this largely depends upon the prime minister being the leader of the largest party in the Commons, which can pass legislation without any or little resistance if they can command the confidence of the House.

This aspect of prime ministerial power is informal and often carried out by the office of Whips, who makes sure that MPs remain loyal and vote on the government line.

King's analysis of contemporary politics showed that some prime ministers often bypass or overrule the cabinet on traditional discussion and to push through their preferred agendas with notable cases such as Margaret Thatcher and Tony Blair.

[74] The ability of the prime minister to influence legislation, according to academic Philip Norton, is often through party discipline and having a reliable majority of MPs who vote in support of the government's priorities.

The prime minister most often would chair cabinet meetings and may determine their frequency, thereby controlling the agenda for policy and steering decisions in their preferred direction.

These are a set of constitutional privileges deriving from monarchial authority that have gradually evolved into tools of executive power managed by the prime minister and the government.

Prerogative powers allow the prime minister to act without the immediate or direct consent of parliament especially in circumstances such as declaring war, deployment of troops and the granting of honours.

[79] Brazier argues that prerogative powers allow the prime minister to act within the "authority of the crown" in situations where neither convention nor statutory law applies.

In recent occasions, the 2003 invasion of Iraq saw Prime Minister Tony Blair deploying British troops to Saudi Arabia without the immediate consent or approval of parliament.

Before the "Glorious Revolution" of 1688, the sovereign exclusively wielded the powers of the Crown; afterwards, Parliament gradually forced monarchs to assume a neutral political position.

[96] If a prime minister (incumbent or otherwise) leads their party to victory in a general election and gains an overall majority in the House of Commons they will be invited by the monarch to form a new government.

[117] These vehicles are often custom made and always British manufactured with in-built gun ports, an independent oxygen supply and the ability to release tear gas to subdue angry crowds.

[121] Historically, the position of deputy prime minister has been created out of political necessity rather than being established by statutory law or convention with the title not being defined in the constitution.

[131] On 6 April 2020, when Boris Johnson was admitted into the Intensive Care Unit of St Thomas' Hospital, when suffering from COVID-19, he asked Dominic Raab "to deputise for him where necessary".

On taking office a new prime minister usually makes a public statement to announce to the country that they have been appointed by the reigning monarch (called "kissing hands").

According to the now-defunct Department for Constitutional Affairs, the prime minister is made a privy counsellor as a result of taking office and should be addressed by the official title prefixed by "The Right Honourable" and not by a personal name.

Through lineage and inheritance, these prime ministers acquired large estates, though they still owned properties in London for political affairs and many used country houses as a retreat.

[161][154][162] In the 21st century, many former prime ministers have set up their own foundations and charities to be used as a platform to continue involvement in political and public issues after they leave office.

[165] Gordon Brown was actively involved in politics long after he left office, most notably during the 2014 Scottish independence referendum, in which he campaigned for the no vote that advocated Scotland to remain in the union.