Three new MPs will be chosen by voters on Thursday – the first time since July 2023 that a trio of Westminster by-elections have taken place on the same day.
The seats up for grabs are Makerfield in Greater Manchester, Aberdeen South in north-east Scotland, and Arbroath and Broughty Ferry in eastern Scotland.
Polling stations are open from 7am to 10pm, with results for all three contests due to be declared in the early hours of Friday.
Here the Press Association looks at the electoral history of each seat and highlights some of the key statistics that could shape the outcomes.
– Makerfield
Labour MPs have represented this area of Greater Manchester for 120 years.
Much of the current seat of Makerfield used to be part of the former constituency of Ince, which was held by Labour without interruption from 1906 to 1983.
Makerfield was created in 1983 and continued the trend of returning Labour MPs to Westminster, the most recent of which was Josh Simons, who was elected in 2024.
The by-election in Makerfield was triggered by the resignation of Mr Simons in order to allow Greater Manchester Mayor Andy Burnham the chance to stand for a seat at Westminster.
Labour’s share of the vote at the 2024 general election was 45%, with Reform UK in second place on 32%, followed by the Conservatives on 11%, the Liberal Democrats on 7% and the Greens on 4%.
This was Reform’s sixth highest vote share in the UK at the 2024 election, behind only Clacton, Ashfield, Boston & Skegness, Great Yarmouth and Barnsley South.
Reform’s candidate in 2024, Rob Kenyon, is standing again this time, along with Mr Burnham for Labour and 12 others, including the Conservatives, the Lib Dems, the Greens and Restore Britain.
Mr Simons’s majority in 2024 was 5,399.
This is smaller than the Labour majority overturned by Reform at the Runcorn & Helsby by-election in Cheshire in May 2025 (14,696), and the Labour majority overturned by the Greens at the Gorton & Denton by-election in Greater Manchester in February 2026 (13,413).
Labour finished 13 percentage points ahead of Reform in vote share in 2024, meaning Reform needs a swing in the share of the vote of just over 6.5 percentage points to take the seat.
This is the equivalent of a net change of seven in every 100 people who voted Labour in 2024 switching directly to Reform.
The 2021 census found 96.7% of the population of Makerfield is white, higher than the equivalent figure for the North West (85.6%) and the UK (83.0%).
An estimated 96% of the population was born in the UK, compared with 88% for the North West and 84% for the UK.
Some 19.3% of children in the constituency were living in poverty in 2024/25 – defined as households with income below 60% of the national median average – which is lower than the figure for the region (24.5%) but similar to the overall level for the UK (19.3%).
The percentage of residents aged 16-64 claiming unemployment benefit stood at 3.1% in April 2026, below the equivalent figure for the region (4.2%) and the UK (3.9%).
– Aberdeen South
The two by-elections taking place in Scotland were triggered when the former SNP MPs in these seats, Stephen Flynn in Aberdeen South and Stephen Gethins in Arbroath and Broughty Ferry, were elected to the Scottish Parliament on May 7.
The law does not allow people to hold seats in the Parliament and in the House of Commons simultaneously.
Aberdeen South has existed as a constituency since 1885 but its boundaries have been redrawn on several occasions and the seat has changed hands across the decades.
In recent times, Labour represented the constituency from 1997 up to 2015, when it was first won by the SNP.
The Conservatives took the seat in 2017, only for the SNP to retake it in 2019 and hold it in 2024.
The result in 2024 saw Mr Flynn elected for the SNP on a very low share of the vote, 33%, with Labour in second place on 25% and the Conservatives close behind on 24%, while Reform got 7%, the Lib Dems 6% and the Greens 3%.
All six of these parties are standing at the by-election, along with a candidate for the Alliance for Democracy and Freedom.
The SNP’s majority in 2024 was 3,758 and the party finished just over eight percentage points ahead of both Labour and the Conservatives.
This means a swing of a little over four percentage points to either Labour or the Tories would see one of those parties take the seat from the SNP.
At the most recent census in Scotland in 2022, 85.5% of the population of Aberdeen South was estimated to be white, lower than Scotland as a whole (92.9%) but higher than the UK (83.0%).
Around 77% of the population was born in the UK, compared with 90% for Scotland and 84% for the UK.
There were 7.8% of children living in poverty in the constituency in 2024/25, lower than the figure for Scotland (12.3%) and the UK (19.3%).
The percentage of residents aged 16-64 claiming unemployment benefit stood at 3.1% in April 2026, the same as for the whole of Scotland (3.1%) and lower than the UK (3.9%).
– Arbroath and Broughty Ferry
The constituency of Arbroath and Broughty Ferry was created at the 2024 general election when it was won by Mr Gethins for the SNP on another low share of the vote, 35%.
Labour finished very close behind on 33%, with the Conservatives in third place on 16%, followed by Reform on 9% and the Lib Dems on 5%.
The seat contains areas of the former constituencies of Dundee East and Angus, both of which had long spells of being represented by the SNP.
Dundee East was held continuously by the SNP from 2005 to its abolition in 2024, while Angus had SNP MPs from 1997-2017 and 2019-2024, with the Tories holding the seat briefly from 2017-19.
Five candidates are standing in the by-election, representing the SNP, Labour, the Tories, the Lib Dems and Reform.
This makes it the least contested of the three constituencies up for grabs on Thursday.
The SNP’s majority in 2024 was just 859.
At the 2022 census in Scotland, 96.8% of the population of Arbroath & Broughty Ferry was estimated to be white, higher than Scotland as a whole (92.9%) and the UK (83.0%).
Around 94% of the population was born in the UK, compared with 90% for Scotland and 84% for the UK.
Some 12.0% of children were living in poverty in the constituency in 2024/25, slightly lower than the figure for Scotland (12.3%) and below the figure for the UK (19.3%).
The percentage of residents aged 16-64 claiming unemployment benefit stood at 3.1% in April 2026, the same as for the whole of Scotland (3.1%) and lower than the UK (3.9%).
