Selby, Somerton and Uxbridge by-elections: Key statistics

It would take a very large swing in the popular vote for all three seats to change hands.

The key statistics behind the three by-elections on July 20 (Jonathan Brady/PA) (PA Archive)

If the Conservatives are beaten at the polls on July 20 in Selby & Ainsty, Somerton & Frome and Uxbridge & South Ruislip, it will be the first time in 55 years that a government has lost three by-elections on the same day.

The previous occasion was March 28 1968, when the Labour government of Harold Wilson was defeated by the Tories in by-elections in Acton, Dudley and Meriden.

Were Rishi Sunak’s Government to lose two of the three contests, the historical benchmark is much more recent: a double defeat of this kind last happened just over a year ago, on June 23 2022, when the Conservatives were beaten at Tiverton & Honiton and Wakefield.

Each of the polls on Thursday presents different electoral and mathematical challenges for both the Government and the opposition parties.

Here are the key statistics for each seat:

– Selby & Ainsty

This North Yorkshire constituency was created at the 2010 general election and has always been held by the Conservatives.

Its former MP Nigel Adams took 49% of the vote in 2010 and pushed up his share at every subsequent poll, taking 53% in 2015, 59% in 2017 and just over 60% in 2019, when he won a majority of 20,137.

Labour came second in 2019 with nearly 25% of the vote, with the Liberal Democrats a distant third on 9%.

While Labour is the main challenger at this by-election, the party faces a tough task to win, requiring a swing in the share of the vote of 17.9 points – in other words, a net change of 18 in every 100 people who voted Tory in 2019 needs to switch sides.

The last time Labour managed a by-election swing of this size or greater was nearly 30 years ago, when it won South East Staffordshire from the Conservatives in April 1996.

There has been one official opinion poll in Selby & Ainsty since the by-election was triggered, putting Labour on 41% of the vote, the Conservatives on 29%, Reform on 8%, the Lib Dems on 6%, the Greens on 6% and the Yorkshire Party on 4%.

However, opinion polls are snapshots, not predictions, and are based on only a sample of voters – in this instance, 502 adults surveyed between June 26 and July 6 by the firm JL Partners.

– Somerton & Frome

Somerton & Frome has a long history of being a two-horse race between the Conservatives and the Liberal Democrats.

The Tories held it from 1983 to 1997 and the Lib Dems from 1997 until 2015, when David Warburton won it back for the Conservatives.

Mr Warburton had a majority of 19,213 at the 2019 election and took nearly 56% of the vote, with the Lib Dems second on just over 26% and Labour third on 13%.

The Lib Dems need a swing in the share of the vote of 14.9 percentage points to come first at the by-election: the equivalent of a net change of 15 in every 100 people switching sides since 2019.

This is a smaller swing than the party achieved when it defeated the Tories at the by-elections in Tiverton & Honiton in June 2022 (29.9 points) and North Shropshire in December 2021 (34.1).

Mr Warburton sat as an independent MP between April 2022 and his resignation in June 2023, after losing the Conservative whip due to allegations of misconduct.

No official polls have been carried out in this Somerset constituency since the by-election was called.

– Uxbridge & South Ruislip

Uxbridge & South Ruislip has been held continuously by the Conservatives since its creation in 2010.

The Tories’ share of the vote has gone up at each successive general election, from 48% in 2010 to 50% in 2015, 51% in 2017 and 53% in 2019.

Former MP Boris Johnson first won the north-west London seat in 2015 and had a majority of 7,210 in 2019.

Labour has always come second in this seat at general elections and polled 38% of the vote in 2019, with the Liberal Democrats on 6%.

To win the by-election, Labour needs a swing in the share of the vote of 7.6 percentage points, or a net change of eight in every 100 people who voted Tory in 2019 switching sides.

This is a smaller shift than the one achieved by Labour in the Wakefield by-election in June 2022, which saw the party win the seat from the Tories on a swing of 12.7 percentage points.

It is also the lowest swing needed for a seat to change hands in any of the three by-elections taking place on Thursday.

There has been one official opinion poll of the electorate in Uxbridge & South Ruislip since the by-election was triggered, putting Labour on 41% of the vote, the Conservatives on 33%, the Lib Dems on 6% and the Greens on 4%.

The poll was carried out by JL Partners among 502 adults between June 26 and July 6.