The UK does not have a formal constitutional role of a deputy or caretaker prime minister who would step in should the prime minister be unable to perform their job for any reason. Prime ministers have usually designated someone to perform duties in the Commons during any absence from the country, for instance appearing at prime minister’s questions (PMQs).
The prime minister is primus inter pares (first among equals) in the UK cabinet system. The UK is governed by the entire cabinet, with individual powers invested in specific cabinet positions. The prime minister holds both formal and informal powers as the most senior adviser to the King, from which some of his or her authority is derived, but can only govern with the support of the cabinet.
There is a hierarchy to the cabinet, which usually denotes the seating order around the cabinet table, and which includes one member of cabinet being designated as ‘first secretary of state’. The title of deputy prime minister has also been used in the past, but neither title has automatically meant that the individual in post would become acting prime minister if anything happened to the incumbent.
Prime ministers continue in office unless they resign or die (or, conceivably, are removed by the King). If a prime minister resigned suddenly or died, and there was a majority government, it would be up to the cabinet to recommend an immediate successor to the King. This could be done with the expectation that his or her role would be temporary, pending the election of a new party leader. However, while political parties usually have the ability to appoint an ‘acting leader’ if the leader resigns or is incapacitated, there is no formal ‘acting prime minister’ role. He or she would be prime minister until they chose to resign or if their cabinet forced them out.
Historically, prime ministers have not designated understudies in advance of who would take over in the event of their falling ill or being otherwise incapable of doing the job. Some prime ministers have had de facto deputies who they rely on closely. However, in recent years, prime ministers have begun to appoint cabinet members as deputies, with the title of deputy prime minister or first secretary of state.
There is no formal power that provides for another minister taking over responsibilities from a prime minister who is incapacitated. Such a role is delegated from the authority of the prime minister and the decision to give them this responsibility in practice needs to be supported by the rest of cabinet. This is because the prime minister’s power is a mixture of informal and political power and precedent.
Secretaries of state hold statutory powers and the prime minister’s executive powers are derived from their role as chief adviser to the King. The prime minister remains the prime minister for as long as they hold the office. Constitutionally, government decisions are made by the cabinet.
On national security matters, the prime minister’s role chairing the national security council can be done by the person deputising for them. Other members of the NSC, including the home secretary and the foreign secretary, oversee the intelligence agencies.
Ministers who may have been appointed to the title of deputy prime minister or first secretary of state will all have different degrees of power within the cabinet, but none provides an automatic expectation that they will take over the prime minister’s position in an emergency.
The title of deputy prime minister has been given to ministers to denote their seniority. It is not filled in every government. Unlike in the US, where the vice president automatically succeeds the president, the deputy prime minister has no formal constitutional powers or ability to replace the prime minister if the prime minister is unavailable. Currently, health secretary Thérèse Coffey also serves as deputy prime minister.
The first secretary of state position is an honorific given to one cabinet member, denoting technical seniority over the other secretaries of state in the cabinet. Some have the title alongside another secretary of state position – Dominic Raab, who held the title from 2019 to 2021, simultaneously led the Foreign Office. Damian Green, first secretary of state for Theresa May, was given responsibilities that could include advising the prime minister on government policy and chairing cabinet committees and taskforces. He acted as a political deputy.
In some cases, the same minister has simultaneously held both positions – from 2001 to 2007, John Prescott was deputy prime minister and first secretary of state in Tony Blair’s cabinet.
In the 2010–15 coalition government William Hague, a Conservative, was appointed first secretary of state and Nick Clegg held the deputy prime minister post as the leader of the smaller coalition party, the Liberal Democrats. However, in the event of the Conservative prime minister David Cameron’s incapacitation, it was expected that Hague or George Osborne, the chancellor, would probably have stepped in as prime minister, rather than Clegg. This was in part because Clegg belonged to a different political party.
Other ministers may perform the role of political deputy to the prime minister, being referred to as a ‘de facto deputy’, without either title of deputy prime minister or first secretary of state. David Lidington served as the minister for the Cabinet Office and chancellor of the duchy of Lancaster under Theresa My, but said that a formal title would have made his job much easier.
Not all political parties have a deputy leader. The Conservative Party does not have a deputy leadership position. Its leadership rules would allow it to appoint a new leader rapidly only if just one candidate stood. If more than one stood it would trigger a leadership contest. The party could appoint a temporary leader in the interim.
The Labour Party has a permanent deputy leader position. However, if a labour prime minister is permanently unavailable, the deputy leader does not automatically take their place. In this scenario the cabinet, in consultation with the Labour Party’s National Executive Committee (NEC), chooses a member of the cabinet to temporarily become prime minister while a leadership election takes place.
Normally, when the prime minister is abroad or on holiday another minister is asked to deputise for them at PMQs and in chairing meetings. This is not always the deputy prime minister or first secretary of state, even if one has been appointed. In this situation, the prime minister is kept informed and is able to perform their job from any location. They will normally have support staff available and would be able to continue the role wherever they are.
During the Cold War, prime ministers began to appoint 'nuclear deputies'. In the event of a nuclear strike, if the prime minister was incapacitated or uncontactable, these deputies would decide what action the UK would take to respond.
There are occasions in the past when past prime ministers have fallen ill and another minister has performed the responsibilities of the prime minister.
In response to the Covid-19 coronavirus outbreak, Boris Johnson named then first secretary of state, foreign secretary Dominic Raab, as his understudy should Johnson become too ill to take on his prime ministerial duties. On 27 March, the PM tested positive for Covid-19 and went into self-isolation in No.10 Downing Street. On 5 April Johnson was taken into hospital. On the evening of 6 April the PM was taken into intensive care and Raab was asked to take on many of the PM’s duties.
In June 1953, the then prime minister, Winston Churchill, reportedly suffered a stroke. Only a few people were made aware of the extent of his illness and the full cabinet was not informed. Churchill’s expected successor, foreign secretary Anthony Eden, was in hospital in New York undergoing an operation. It is thought that had Eden been in better health at the time, he would have immediately succeeded Churchill as prime minister. Instead, Churchill carried on his prime ministerial duties as normal, surprising doctors by recovering his strength over the following months.
On 11 May 1812, the prime minister Spencer Perceval was assassinated. On the recommendation of the cabinet, he was replaced by Lord Liverpool. However, after the government lost votes in parliament, Liverpool was not confirmed as prime minister until 8 June.
The US constitution dictates that if the president dies, resigns or is removed from office, the vice president takes on presidential powers and duties. There was initially some debate about whether the vice president is simply acting as president or has become president. This was settled by section one of the 25th amendment to the constitution, which states that if the president is incapacitated, the vice president immediately becomes president, rather than ‘acting’ president. Nine vice presidents have taken over the presidency mid-term.
In Canada, the role of deputy prime minister is ceremonial, and the incumbent took office in 2019 after a 13-year period in which no one held the post. If the Canadian prime minister is permanently unavailable, the deputy prime minister does not automatically take control. Instead, the governing party nominate a member of their caucus to take the position, and this nominee is appointed by Canada’s governor-general. The deputy prime minister is eligible to be selected by the governing party as their nominee.
In Australia and New Zealand, the deputy prime minister role is held by the deputy leader of the largest party, unless the government is in coalition, when the post is held by the leader of the second largest party in coalition. If the prime minister is incapacitated, the governor-general, the representative of the monarch in the country, appoints the deputy prime minister as prime minister on a temporary basis, until the governing party elects a new leader.