UK by-election results: Everything you need to know in graphs

Key facts and statistics from the results of Thursday’s by-elections

Rishi Sunak has suffered a double by-election defeat in safe Tory seats, with Labour and the Liberal Democrats both overturning majorities of about 20,000.

Labour won Selby and Ainsty and the Lib Dems took Somerton and Frome on sizable swings which will leave many Tory MPs looking nervously at their own majorities.

But the Tory leader was spared the prospect of being the first prime minister since 1968 to lose three by-elections on the same day as Labour failed to secure victory in Boris Johnson’s former seat of Uxbridge and South Ruislip.

Here are some of the key facts and statistics from the results of Thursday’s by-elections:

– Selby and Ainsty

(PA Wire)

Labour’s victory at Selby and Ainsty has made history: it is the largest Conservative majority (20,137) overturned by the party at a by-election since 1945.

The previous record was set at the Mid Staffordshire by-election in March 1990, when Labour overturned a Tory majority of 14,654.

To win the seat, Labour needed a swing in the share of the vote of 17.9 percentage points: the equivalent of a net change of 18 in every 100 people who voted Conservative at the 2019 general election switching sides.

They managed a swing of 23.7 points: the largest achieved by Labour at by-election since it won Dudley West from the Tories in December 1994 (29.1 points) and the second largest swing managed by Labour at a by-election since 1945.

The Conservative share of the vote in Selby dropped sharply from 60% at the 2019 general election to 34%, while Labour’s share rose from 25% to 46%.

The winner, 25-year-old Keir Mather, will become the youngest MP in the House of Commons.

– Somerton and Frome

(PA Wire)

Somerton and Frome is the fourth seat the Liberal Democrats have taken from the Conservatives at a by-election since the 2019 general election, all of which have changed hands on huge swings in the vote.

The swing at Somerton was 29.0 percentage points, or the equivalent of a net change of 29 in every 100 people who voted Tory in 2019 switching sides.

This is well above the 14.9 point swing the Lib Dems needed to win the seat.

It beats the swing the party achieved when they defeated the Conservatives at the by-election in Chesham and Amersham in June 2021 (25.2 points) and is just below the swing when they gained Tiverton and Honiton from the Tories in June 2022 (29.9 points).

The party managed an even bigger swing when they defeated the Conservatives at North Shropshire in December 2021 (34.1 points).

Sir Ed Davey is the first leader of any political party to win four by-elections since Paddy Ashdown – founding leader of the Lib Dems – did so in the early 1990s.

The Conservatives were defending a majority at Somerton of 19,213 and it is one of the largest of its kind to be overturned at a UK by-election since 1945, sitting just outside the top five.

The result means the Lib Dems have regained a seat they first won at the 1997 general election and then held for 18 years – one of a number of constituencies in south-west England that once made up the party’s “yellow wall”, which was wiped out by the Conservatives in 2015.

However, new Lib Dem MP Sarah Dyke will soon face a fresh challenge, as Somerton and Frome is one of a number of seats being abolished at the next general election due to boundary changes.

It is being split in two to form the new constituencies of Glastonbury and Somerton and Frome and East Somerset.

– Uxbridge and South Ruislip

(PA Wire)

Labour needed a swing in the share of the vote of 7.6 percentage points to win Uxbridge and South Ruislip from the Conservatives, but fell short and managed only 6.7 points.

This is well below the 12.7 point swing Labour achieved at the Wakefield by-election in June 2022, when they won the seat from the Tories.

Labour did manage to cut the Conservative majority at Uxbridge from 7,210 at the 2019 general election to just 495, while the Tory share of the vote fell from 53% in 2019 to 45%.

Labour’s share of the vote rose from 38% to 44%.

Uxbridge and South Ruislip has been held continuously by the Conservatives since the seat was created in 2010 and new MP Steve Tuckwell is the third Tory to represent the area, after John Randall and former prime minister Boris Johnson.