How many seats do Labour and the Tories need to win?

The Labour Party will need an historic swing to win a majority at the next general election, with the party's path to victory made more difficult by boundary changes.

Keir Starmer will need a swing of 12.7% to form a majority government in the next election, according to new analysis. That is larger than the 10.2% swing former prime minister Tony Blair achieved when he led Labour to power in 1997, "and more than double the change achieved at any other election since 1945", said Bloomberg.

The data, compiled by academics Colin Rallings and Michael Thrasher for ITV, Sky, BBC and the Press Association, looked at how boundary changes introduced since the 2019 election might affect the Labour Party's chances of victory.

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How many seats are needed for a parliamentary majority?

To win a majority in Parliament, a party needs to secure one more seat than the combined total of all other parties. With 650 seats to be won, the magic number is 326.

The size of the majority is the number of extra seats the winning party has. If one party won 326, then the number of seats held by other parties would be 324 and the majority would be two.

How many seats do the Conservatives hold right now?

The Conservatives, who won 365 seats in the 2019 election, currently hold 349 due to a number of resignations, suspensions, defections and by-election defeats, so they have an effective working majority of 57.

This number also takes into account the number of non-voting MPs in Parliament. Irish nationalist party Sinn Féin holds seven seats, but has a long-held tradition of not attending the Commons, while the Speaker and their three deputies are also excluded from voting.

And what about Labour?

In contrast, the Labour Party won 203 seats in 2019, but like the Conservatives, has since seen its numbers fall since, to 197. 

Despite suffering its worst defeat since 1935 in the 2019 general election, recent polling indicates that Labour, under Starmer's leadership, is on track to win a substantial 120-seat majority. 

A YouGov poll of 14,000 voters suggested Labour is on course to win 385 seats, while the Conservatives might see a collapse to as few as 169.

What do the new boundary changes mean for Labour?

The challenge facing Labour has been made more difficult by new boundary changes, with the UK's 650 constituencies redrawn to account for population shifts and to equalise voter numbers.

Following the 2019 election, Labour initially needed a direct swing of 7 percentage points from the Tories to achieve a hung parliament. 

However, with the boundary changes, this requirement has increased to 8.3%. For an overall majority, Labour's swing requirement has risen from 12 to 12.7 points.

While the analysis suggests that any uniform swing from Conservatives to Labour between 4.2% and 12.7% could result in a hung parliament, that is made on the assumption that there will be no change in the votes cast for other parties – "which is highly unlikely to be true", said The Independent. 

For example, according to Rallings and Thrasher, a 10-point swing from the SNP to Labour could lead to Starmer gaining 15 seats under the new boundaries, easing his path to Downing Street.