The powers of the prime minister of the United Kingdom come from several sources of the UK constitution, including both statute and constitutional convention, but not one single authoritative document. They have been described as "...problematic to outline definitively."
The UK has a fusion of powers, which means that the prime minister exercises functions in both the executive and the legislature. This also means that accountability between the branches is limited, as it is difficult to check on oneself. The prime minister normally (but not necessarily) leads the largest party in the House of Commons and they usually have some power over their own party due to that role.
The status and executive powers of the British prime minister means that the incumbent is consistently ranked as one of the most powerful democratically elected leaders in the world.
Definition of the role and its powers
Between 2011 and 2014, the Political and Constitutional Reform Select Committee conducted an inquiry into the 'role and powers of the Prime Minister'. In their report, they wrote: When Lord Hennessy gave evidence to us, he commented: "the role of the Prime Minister is like the British constitution as a whole—you think you are getting close and it disappears into the mists." With the role itself difficult to define, it is not surprising that the powers of the person who fulfils the role are similarly problematic to outline definitively. Most powers exercised by the Prime Minister are not defined in statute and cannot be found in one place. In his book The Prime Minister: The office and its holders since 1945, Lord Hennessy stated: "Arguments have raged around the powers of the British Prime Minister for nearly 300 years."
Without a clear definition of the role of prime minister, the powers associated with the office have been able to evolve and accumulate, unhindered by statute, over hundreds of years...
There is no single authoritative source for what the role involves and the powers the prime minister can exercise.
Documents describing the role and powers of the PM include: From 1947 to 1948, the Cabinet Office prepared a paper titled 'Function of the Prime Minister and his Staff'. In 2002, a private member's bill was drafted to define the 'office, role and functions' of the PM, but this was never passed. In 2011, the Cabinet Office published The Cabinet Manual, setting out the main laws, rules and conventions affecting the conduct and operation of government, including a description of the role of the PM. In 2011, Peter Hennessy gave a list of 47 functions, under eight headings, of the prime minister. In 2014, the Political and Constitutional Reform Select Committee produced a final report to their Inquiry, titled Role and powers of the Prime Minister.
Executive powers
Appointing ministers
When commissioned by the sovereign, a new prime minister's first requisite is to "form a Government" – to create a cabinet of ministers that has the support of the House of Commons, of which they are expected to be a member. The prime minister nominates all other cabinet members to the sovereign for appointment (who then, if they are not already, names them Privy Counsellors) and ministers, and although consulting senior ministers on their junior ministers, without any Parliamentary or other control or process over these powers. The prime minister decides the ranking order of all ministers.
The prime minister holds powers of patronage which means that at any time, the PM may obtain the appointment, dismissal or nominal resignation of any other minister. The PM may implement a cabinet reshuffle; one famous example was the Night of the Long Knives (1962). The PM may resign, either purely personally or with the whole government. A prime minister is no longer just "first amongst equals" in HM Government; although theoretically the Cabinet might still outvote the prime minister, in practice the prime minister progressively entrenches their position by retaining only personal supporters in the Cabinet. In occasional reshuffles, the prime minister can sideline and simply drop from Cabinet the Members who have fallen out of favour; they remain Privy Counsellors, but the prime minister decides which of them are summoned to meetings.
The prime minister is responsible for producing and enforcing the Ministerial Code.