UK
Constituency boundary changes give Keir Starmer a tougher route to Number 10 – find out why with our swingometer
Labour faces an even tougher challenge to win the next general election after changes to the UK’s constituency boundaries.
The party was already aiming at a record swing of 12 percentage points from the Conservatives, better than Tony Blair achieved in 1997, to secure a majority.
Now, calculations by election experts Colin Rallings and Michael Thrasher for Sky News, PA, BBC News and ITV News suggest that when the public heads to the ballot box later this year, the target swing will be one of 12.7.
Rallings and Thrasher, who produced equivalent estimates for the 1997 and 2010 boundary reviews, estimated what the 2019 general election result would have been if it had been fought in the new constituencies.
Their findings, which will form the notional starting point for the next contest, increase the Conservative majority from 80 seats to 94. The Conservatives will defend 372 seats, up from 365, while Labour’s tally reduces from 203 to 201 seats.
The other parties to lose seats are the Liberal Democrats who drop from 11 to just 8 seats, matching their lowest total from 2015, and Plaid Cymru, which loses two of its four seats.
Those three Lib Dem losses are among a group of five constituencies to retain the same name but switch to a different party under the estimated results. It means former Lib Dem leader Tim Farron becomes the challenger, as well as the current MP, in Westmorland and Lonsdale.
Read more: The constituencies and voters Starmer needs to win over to become PM
Postcode search: Find out the new constituency you’re in and how it’s changed
How boundary changes make Keir Starmer’s job even harder – and what he needs to become PM
Boundary changes: How the electoral impact of the new political battlegrounds are calculated
What effect will this have on the election?
The increased Conservative advantage makes the hill steeper to climb for Labour.
The key figure is 326 – that is the number of seats needed for a majority.
That means a net loss of 47 seats for the Tories – up from 40 pre-boundary changes – would oust them from Number 10, and a net gain of 125 seats would deliver Labour an overall majority of two.
If voters across the country behaved in the same way, switching from Conservative to Labour, then Buckingham and Bletchley in the South East of England would be the seat necessary to fall to give Sir Keir Starmer the keys to Number 10.
If that happens, Labour would have achieved a record swing of 12.7 – larger than the 10.2 point swing from the Tories that Tony Blair achieved with his landslide victory in 1997, and more than double the swing achieved at any other election since 1945.
A 4.2 point swing to Labour would see the Conservatives lose their overall majority – with the key seat of Wrexham in North Wales being the one Sir Keir would have to take in order to achieve that.
The boundary changes also raise the benchmark for Labour to become the largest party in a hung parliament. That swing is now 8.3 points from Conservative to Labour, rather than 7. The pivotal seat in this scenario is Chelsea and Fulham.
Read more:
When could the next general election be?
What about the other parties?
Of course, it will not just be Labour versus Conservatives on the night, and the performance of other parties could play a significant role in who comes out on top.
A key factor for Labour’s success will be in its battles against the SNP in Scotland, as wins here would lower the gains needed from the Tories.
In total, ten of the SNP’s 48 seats have majorities of less than 10%. Labour is second in just two of these – Lothian East and Cowdenbeath and Kirkcaldy.
Those would require a 5 point swing from SNP to Labour. But current polling suggests a swing of 12 points, which could see Labour gain as many as 23 seats from the SNP.
To put that in context, not since the 1950s has Labour formed a government at Westminster with less than 40 of its MPs elected in Scotland. To achieve that under the new boundaries would require a massive 25.1 swing from SNP to Labour.
Lib Dem gains from the Conservatives could also ease Labour’s path to Downing Street. The new estimates mean they start second to the Tories in 85 constituencies, with 40 of those in the South East and a further 25 in the South West of England.
The most marginal of the 85 seats is Carshalton and Wallington in London.
Which MPs are at risk?
Arguably the most high-profile Conservative in Lib Dem sights is Chancellor Jeremy Hunt, who would lose Godalming and Ash in the South East – if there was a swing of at least 9.6 points to the Lib Dems.
Sir Ed Davey’s party requires smaller swings to defeat the justice secretary, Alex Chalk, in Cheltenham (1.2 points) and the health minster Maria Caufield in Lewes (3.7 points).
If Levelling Up Secretary Michal Gove stands in Surrey Heath then a 14.9 point swing to the Liberal Democrats would see him lose the seat.
Several former and current Conservative ministers also have a tough task against Labour to stay in parliament.
For example, a swing of just 1.5 points in Chingford and Woodford Green would see former Tory leader Sir Iain Duncan Smith lose his notional 1,604 majority to Labour.
If Northern Ireland minister and leading Brexiteer Steve Baker chooses to defend the adjusted Wycombe seat, the 1,494 notional majority would be wiped out by a 1.6 point swing to Labour.
And a swing of 3.6 points to Labour in Chipping Barnet would oust former minister Theresa Villiers, despite her majority of over 4,000 votes.
Even if Labour doesn’t reach the magic 12.7 point swing for a majority, other key Tory figures could fall as a result of a much smaller one, including ex-justice secretary Sir Robert Buckland, deputy chairman Lee Anderson and Defence Secretary Grant Shapps, if he contests Welwyn Hatfield.
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While current polling suggests a sizeable Labour parliamentary group, there are some tight contests for that party’s figures too.
A total of nine seats would fall to the Conservatives on a swing of less than one percentage point from Labour.
A swing of just 1.3 points to the Tories in Pontefract, Castleford and Knottingley would defeat shadow home secretary Yvette Cooper, while a 2.9 point swing would see shadow policing minister Alex Norris lose Nottingham North and Kimberley to the Tories.
Some Labour MPs, including Chris Elmore (Bridgend) and Emma Hardy (Hull West and Hessle), also find themselves challenging in what are now notionally Conservative seats.
All the above is based on estimates and it is impossible to know precisely how these new constituencies voted in 2019. It is also tricky to determine the impact of the decision by the Brexit party not to contest most Conservative seats in 2019.
A full methodology of the notional results estimates used by Rallings and Thrasher can be accessed here. The underlying data on all of the new vote estimates for each constituency can be downloaded as a spreadsheet.