How powerful is a supermajority in the House of Commons?

As Conservatives continue to raise concerns about untrammelled power if Labour wins a landslide, how do large majorities work in the UK?

– What is a ‘supermajority’?

With opinion polls showing a significant Labour advantage in the 2024 General Election, some Conservative politicians – including Prime Minister Rishi Sunak – have warned this could create a “supermajority” in the House of Commons for Sir Keir Starmer.

It is a term usually associated with politics in the United States, and refers to situations where more than a simple majority of half of the votes available plus one is required in a ballot. For example, a debate can be brought to a premature end and a vote forced by 60 US senators (out of the 100 total), while a two-thirds Senate supermajority is required to ratify treaties.

Scottish politics also recognises supermajorities constitutionally, with laws that affect the election of MSPs being potentially subject to this restriction. A Scottish supermajority requires two-thirds of MSPs to vote in favour.

Policing minister Chris Philp said in one interview that an “enormous majority” would be “in the dozens or even in the hundreds”. With 650 seats for MPs in the Commons, a party would need to win 434 to hold two-thirds – a majority of 218.

But the House of Commons has no provisions for any laws requiring anything beyond a simple majority to be passed.

The largest Commons majority after an election was in 1924, when Stanley Baldwin’s Conservatives held a majority of 210 seats.

British Politics – The Conservative Party – Prime Minister Stanley Baldwin – Ellesborough – 1923 — Then-prime minister Stanley Baldwin at Chequers, the PM’s official country residence (PA)

The Conservative Party has claimed that a Labour “supermajority” would be “unstoppable”, but in theory a British government with a majority of 10 MPs is no different from one with a majority of 100 MPs. Both are able to control the legislative agenda and pass laws with a majority vote.

In practice, narrow majorities are vulnerable to rebellions by backbenchers or unexpected by-elections, with larger majorities helping party leaders to lessen the impact of these threats.

The official Opposition – the second-largest party in the Commons – therefore often struggles to beat government-backed motions, and instead scrutinises legislation through debates and its presence on various committees overseeing departments.

However, the larger the majority, the fewer MPs the Opposition will have to perform this scrutiny. Not only does this affect how many people are available to attend debates, but the number of questions at Prime Minister’s Questions and the chairing of select committees are allocated in proportion to a party’s share of seats.

Following the 2019 election, Labour as Opposition was entitled to nine committee chairs, compared with 16 Conservative and two for the third-largest party, the SNP.

Sudan unrest — Defence Secretary Ben Wallace giving evidence to the Defence Select Committee (House of Commons/UK Parliament/PA)

At the last election in 2019, Boris Johnson won a majority of 80 seats (365 constituencies against 285 represented by every other party), which he hailed in a victory speech as “the biggest Conservative majority since the 1980s”. But because of defections, by-elections and suspensions, the Conservative majority before the 2024 election was called had fallen to 42 (with 346 seats still held).

In 1997, Tony Blair won 418 seats (out of a possible 659) to deliver a Labour government with a majority of 179. This comfortable level of victory allowed the party to enact significant and lasting measures, including the creation of the minimum wage and devolution of powers to Scotland, Wales and Northern Ireland.

Mr Blair won smaller majorities at subsequent elections but having started from such a peak they were still significant – standing at 167 in 2001 and 66 in 2005. A Parliamentary vote on the UK joining the war in Iraq in 2003 saw 84 Labour MPs rebel, which would have been enough to defeat the motion if most Conservative MPs had not lent their support.

After a moderate majority of 43 in 1979, Margaret Thatcher’s next election wins delivered large majorities (144 in 1983 and 102 in 1987). With the size of her majority, Mrs Thatcher’s 11 years in power saw only one government Bill defeated in the House of Commons – a 1986 proposal to legalise the opening of shops on Sundays, which was rebelled against by 72 Conservative MPs on largely religious grounds.