The Prime Minister and Cabinet

The prime minister is 'chief executive' of the government, holding an office that is largely based on convention. 

As the power of the monarch steadily declined to the ceremonial role recognisable today, the prime minister's role expanded to replace it. 

There is no fixed point at which the role of the prime minister came into existence. Instead, powers have emerged or evolved in a number of ways: 

• Assuming the royal prerogative. 

• Assimilating powers by convetion. 

Most prime ministerial powers were formerly exercised by the monarch. 

Known as 'royal prerogative' powers, these have been transferred to, or incorporated by, the prime minister over many years.

They include:

• Controlling the armed forces.

• Declaring war.

• Signing treaties.

• Appointing and dismissing ministers.

• Organising the civil service.

In the absence of a codified constitution, certain powers have been assumed by convention.

Party and parliamentary practices such as the expectation of party support via collective cabinet responsibility have evolved to sustain the position of the prime minister. 

One of the most significant principles of the US Constitution is the doctrine of the separation of powers. 

In its first three Articles, the Constitution sets out clearly the roles and responsibilities of the three branches of government and how they check and balance each other. 

Within Article II, the precise nature of executive power is detailed along with the limitations upon it. For example, the President has the power to sign treatis but 'only provided 2/3 of the Senators concur'. 

Section 3 requires the president to 'give to the Congress information on the State of the Union'.

Section 4 explains how and when a 'president shall be removed from Office on Impeachment'. 

1. Be an MP.

One of the prerequisites of becoming a prime minister is that the office holder is drawn from the Houses of Parliament. 

2. Be the leader of the largest single party in the Commons.

The most important element of prime ministerial power is their leadershipo of the largest party in the Commons. 

When a prime minister no longer holds such a role, their tenure is over. Margaret Thatcher was forced to resign as prime minister when she withdrew from the Conservative Party leadership contest in 1990. 

Unlike with the US President, there is no definitive list of roles or duties that explains or clarifies the office of the prime minister.

Broadly speaking:

• The prime minister is the most senior minister within the government - the chief executive - and chairs the cabinet as primus inter pares (first among equals).

• The prime minister is the head of government and acts as the head of state in most circumstances, providing national and international leadership. 

• As leader of the largest party in the Commons, the prime minister is chief legislator and controls much of the parliamentary agenda. 

• The prime minister represents the UK in world affairs, deploys the armed forces and is chief diplomat, with powers to sign international treaties. 
  

The Prime Minister's office is headed by nearly 200 civil servants or political appointees.

The main functions are: 

• Communication: with intense media focus on the prime minister, effective communication of government policy and prime ministerial positions is of paramount importance. 

• Advice: the Prime Minister's Office is the coordinator of policy advice to enable the prime minister to set the strategic direction of the government and scrutinise the work of the departments of state. 

1. Power of appointment

The prime minister exercises the prerogative powers of appointment and dismissal of all senior members of the government - cabinet ministers, senior civil servants, peers, bishops and judges. 

Such patronage powers are extensive, command significant loyalty and enable the PM to promote and demote key allies or rivals. 

2. Directing the government

Setting policy objectives, short and long-term strategic goals and determining the cabinet agenda are key prime ministerial responsibilities. 

3. Managing Parliament.

The leadership of the majority party in the House of Commons is central to the prime minister's power. 

Control of the parliamentary timetable and expectations of party loyalty remain powerful prime ministerial tools. 

Fixed-term parliaments have largely removed the ultimate threat of dissolution. 

4. National and international leadership.

In times of crisis, the prime minister is expected to provide leadership - a role that is magnified in an era of intense media scrutiny. 

On a practical level, exercising the prerogative powers of waging war and signing treaties enhances the PM's standing and prestige. 

Primus inter pares

While prime ministers will want to reward those who have supported their rise to the top, ignoring or marginalising others can lead to difficulties. 

The ways that the actions and behaviour of senior colleagues limit the prime minister are:

1. Resignation

Margaret Thatcher lost the support of her party and the public, but it was the resignation of her Chancellor of the Exchequer, Geoffrey Howe, that finally led to her departure in 1990. 

2. Criticism

The highlighting of Tony Blair's cabinet 'control freakery' by Labour's Mo Mowlam was particularly damaging around the time of her departure from frontbench politics in 2001. 

3. Opposition

Michael Gove's frustration at being removed from the role of Education Secretary in 2014 is widely thought to have been behind his opposition to David Cameron in the 2016 EU referendum. 

Party

Controlling the largest party in the Commons is a vital element of prime ministerial power. 

While control of senior party colleagues is one thing, keeping backbenchers supportive and energised can be another thing entirely.

• Resentment on the backbenches prompted Anthony Meyer's 'stalking horse' leadership challenge of Thatcher in 1989, an act that revealed deep-seated opposition to the party leader from within.

• Sustained backbench criticism irreversibly undermined Gordon Brown's authority in the run-up to 2010. 

Parliament

The accountability function of Parliament requires the prime minister to face weekly questioning and be subject to the scrutiny of select committees.

Legislative defeat is rare and can be harmful to a PM's reputation when it occurs.

• David Cameron's first major Commons defeat - on EU spending in October 2012 - prompted a change of policy over Europe. 

• An appearance before the Commons Liaison Committee in December 2016 prompted Theresa May to provide greater clarity on plans for parliamentary consultation over Britain's withdrawal from the EU. 

People

Damaging opinion poll data, defeats in by-elections or disappointing local election performances can prove a significant check on prime ministerial power. 

• After backing 'Remain' ahead of the EU referendum, Cameron felt compelled to resign his prime ministerial position after defeat. 

• The 2017 general election proved disastrous for May's leadership. Despite increasing the Tory vote (up 5.5% on 2015), the loss of 13 seats and the party's pre-election Commons majority were seen as an indictment of her uncharismatic and aloof campaign.