What happens if a prime minister loses their seat in a general election?

The prime minister is elected like any other MP. At every general election there is a possibility, however remote, that the incumbent governing party could remain the largest in the House of Commons but that their leader would not be returned to parliament. 

Has a prime minister ever lost their seat?

No incumbent prime minister has ever lost his or her seat at a general election.

Rishi Sunak, the current prime minister, is standing for re-election in the Richmond and Northallerton constituency. At the last election, his majority (in the Richmond constituency, which had slightly different boundaries) was 27,210. 

Of recent prime ministers, Boris Johnson’s majority of 7,210 in Uxbridge and South Ruislip in the 2019 election is the smallest. Even at its lowest point, Margaret Thatcher’s relatively small numerical majority in Finchley translated into a 20-point lead over the Labour candidate in the constituency.

Two prime ministers have come close to losing their seats. In December 1905, Arthur Balfour resigned as prime minister in an attempt to force an election, but the leader of the opposition, Henry Campbell-Bannerman, instead formed a government and became PM. Balfour went on to lose his constituency at the election a month later. In the 1935 general election, Ramsay MacDonald was defeated, having resigned as head of the national government not long before the campaign started. 

Have other party leaders ever lost their seats?

Balfour was technically the first leader of the opposition in the 20th century to lose his seat at a general election. Herbert Asquith was the second – he was defeated in 1918 and again in 1924 (having returned to parliament in the interim via a by-election in Paisley). At the 1931 election, Arthur Henderson, leader of the Labour Party, lost his seat during the landslide victory of the national government led by his former party colleague Ramsay MacDonald. Since then, no leader of the opposition has ever lost their seat in a general election.

Leaders of smaller parties have lost their parliamentary seats 18 times since the turn of the 20th century. The Liberal Party lost seven leaders between 1918 and 1979. The most recent example of the phenomenon came in 2019, when the leader of the Liberal Democrat Party, Jo Swinson, failed to win re-election in East Dunbartonshire. 

Could a prime minister remain in post if they lost their seat?

The first issue is whether the defeated prime minister’s party is in a majority or clearly able to command the confidence of the Commons; or if another party is able to do so. If another party can and is invited to form a government, its leader would become prime minister and so make the situation of the defeated prime minister moot. 

But if the defeated PM’s party still had a majority or could clearly command the confidence of the Commons, and will form a government, then three further factors come into play:

• Can they remain as party leader?
• Does a PM need to be a party leader?
• Does the PM need to be an MP? 

Can a defeated prime minister remain leader of their party?

The Conservative Party constitution says that the leader of the party "shall be drawn from those elected to Parliament". Clause VII of the Labour Rule Book also says its leader "shall be elected from among Commons members of the PLP [Parliamentary Labour Party]." Neither says explicitly that a leader who was no longer an MP would have to resign. 

How party leadership rules are interpreted might depend on the level of support the defeated prime minister retained among their MPs and party membership. If a prime minister resigned as party leader, their party would have to organise a leadership election according to their own rules (unless, in the Conservative Party, the 1922 Committee of backbench MPs determined there was only one candidate). 

Among smaller parties, it is quite common for party leaders not to sit in the House of Commons. The leaders of the Scottish National Party, Plaid Cymru, DUP, Social Democratic and Labour Party, Ulster Unionist Party and Sinn Féin are all elected in their respective devolved institutions. The Green Party’s two co-leaders are not elected MPs.

Does the prime minister need to be party leader? 

The Cabinet Manual says that a PM "will normally be the accepted leader of a political party that commands the majority of the House of Commons", but it does not say that this must be the case.

Does the prime minister have to be an MP?

The process of appointing the prime minister assumes that he or she will sit in the Commons, but there is nothing that says what happens if they cease to be an MP. The prime minister is the King's minister. Precedent suggests that a prime minister should be an MP, but there is no suggestion that they must immediately resign if they lost their seat.  

The Cabinet Manual states that the prime minister “always sits in the House of Commons.” However, this mostly relates to the question of whether they should sit in the Commons rather than the House the Lords.

Although prime ministers regularly sat in the House of Lords in the 18th and 19th centuries, governing from the Commons has been convention since 1902. In 1963 Alec Douglas-Home resigned his peerage and entered the Commons via a by-election when he became leader of the Conservatives.

However, prime ministers are expected to be accountable to parliament through Prime Minister’s Questions, delivering statements and appearing in front of the Liaison Committee. It would therefore not be sustainable for a prime minister to stay in office without being an MP indefinitely.

Can other defeated ministers stay in office?

As no incumbent prime minister has ever lost their seat at a general election, other ministers are the best source of constitutional precedent. It is rare for ministers, particularly Cabinet ministers, to lose their seats:  12 serving Cabinet ministers have lost their seats since 1974. On 11 occasions, this happened during elections that produced a change of government  - Chris Patten, in 1992, is the exception. When the election has a clear outcome, defeated ministers resign immediately. 

In the early days of a hung parliament, ministers do stay in office without being MPs. In 2010, Jim Knight, then minister of state for employment and welfare reform at the Department for Work and Pensions, lost his seat at the election, but stayed on at DWP until the new government was formed. Similarly, after the general election of 1974, Gordon Campbell continued to serve for a week as secretary of state for Scotland despite losing his Moray and Nairn seat.

During election campaigns there are no MPs because parliament is dissolved but government ministers, including the prime minister, remain in place. 

The PM’s constitutional status is similar to other ministers, which suggests that he or she could also remain in office temporarily if they lost their seat. 

Who would take over in the event of resignation? 

There is no mandated order of succession for prime ministers – the position is dependent on the confidence of the House of Commons and appointment by the King. If a PM resigned, having lost his or her seat, another PM would need to take over immediately. This could be an interim figure sitting until a leadership contest had been held by the governing party. However, in a minority government, recommending a prospective prime minister to the Palace would be dependent on whether that figure could command the confidence of MPs. 

In the event that a Labour prime minister lost his or her seat but the party won a majority, the deputy leader would take their place in Number 10 until a leadership election could be organised. When Labour leader John Smith died in May 1994, deputy leader Margaret Beckett served as leader of the opposition until Tony Blair’s election on 21 July 1994.

In the Conservative Party there is no official second-in-command position. If the party held a majority, the Cabinet could nominate an interim prime minister, then its MPs could choose a permanent successor in a leadership contest. If MPs rallied around a single candidate in a leadership contest, then that person could take over very quickly. If the Conservatives did not have a majority, it is much more complicated; it would depend on whether that successor is likely to be able to command confidence. 

What if there was a hung parliament?

If the election did not result in a clear majority then the defeat of a prime minister might affect whether their party could form a government. Current constitutional practice favours an incumbent PM, and he or she has the opportunity to test whether they can command confidence through a King’s Speech. If another MP from the incumbent party was needed to lead the new government, this incumbency preference would not automatically apply. 

On the other hand, constitutional practice around hung parliaments is also a reason why a PM might remain in office for a period despite losing their seat. There must be a prime minister in place, so if no replacement was obvious, the incumbent PM might stay on regardless of not holding a seat in the Commons, while parties establish who could command confidence and form a new government.