What is a supermajority and why do the Tories keep talking about it?

With Labour leading significantly in the polls, Prime Minister and Tory leader Rishi Sunak launched a 24-hour countdown campaign on X to prevent what he calls a "Labour supermajority” led by Sir Keir Starmer.

The term 'supermajority', usually associated with US politics, refers to needing more than a simple majority to win a vote. In Scotland, some laws, particularly those affecting the election of MSPs (Members of the Scottish Parliament), require a supermajority, meaning two-thirds of MSPs must vote in favour.

Policing Minister Chris Philp said in an interview that an "enormous majority" would mean winning by dozens or even hundreds of seats. With 650 seats in the Commons, a party would need 434 seats to hold a two-thirds majority, a margin of 218 seats.

However, the House of Commons does not require more than a simple majority for any law to be passed.

The largest post-election majority was in 1924 when Stanley Baldwin’s Conservatives held a majority of 210 seats.

How powerful is a party with a supermajority?

The Conservative Party has claimed a Labour supermajority would be "unstoppable."

However, in theory, a British government with a majority of 10 MPs is no different from one with a majority of 100 MPs, as both can control the legislative agenda and pass laws with a majority vote.

But, narrow majorities are vulnerable to rebellions by backbenchers or unexpected by-elections. Larger majorities help party leaders lessen the impact of these threats.

As the second-largest party in the Commons, the opposition often struggles to defeat government-backed motions. Instead, it scrutinises legislation through debates and its presence on various committees overseeing departments.

However, a larger majority means fewer MPs from the opposition are available for scrutiny.

This impacts attendance at debates, but allocations for Prime Minister’s Questions and chairing select committees are proportionate to each party’s share of seats.

After the 2019 election Labour, as the opposition, held nine committee chairs compared to 16 held by the Conservative Party and two by the third-largest party, the SNP.

Which governments have previously ruled with large majorities?

Following the 2019 General Election, Boris Johnson celebrated a majority of 80 seats (365 constituencies compared to 285 held by all other parties), marking it as "the largest Conservative majority since the 1980s" in his victory speech.

Due to defections, by-elections, and suspensions, the Conservative majority before the 2024 election had decreased to 42 seats, with 346 seats still held by the party.

In 1997, Tony Blair secured 418 seats out of a possible 659, giving Labour a government with a substantial majority of 179.

This decisive victory enabled the party to implement significant and enduring reforms, such as establishing the minimum wage and devolving powers to Scotland, Wales, and Northern Ireland.

After his initial landslide victory, Blair secured smaller majorities in future elections, standing at 167 in 2001 and 66 in 2005.

During a parliamentary vote on the UK joining the Iraq War in 2003, 84 Labour MPs rebelled, a number that could have defeated the motion if most Conservative MPs had not supported it.

After initially winning a moderate majority of 43 seats in 1979, Margaret Thatcher's subsequent election victories delivered larger majorities, 144 seats in 1983 and 102 seats in 1987.

With such substantial backing, Thatcher's 11-year tenure saw only one government Bill defeated in the House of Commons - a 1986 proposal to legalise Sunday shopping, which faced rebellion from 72 Conservative MPs largely on religious grounds.

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