The election battlegrounds

Realistically there are four main battlefields in the general election. First is that between Conservative and Labour, which is the battle that will really determine how large the Conservative majority is (and how badly Labour are damaged by an election fought when they are at a historic low). Next there are the Lib Dem battles, against Labour and against the Conservatives -

polls and by-elections suggest the Lib Dems are staging a recovery, but what is the potential to convert that into seats? Finally there is the position in Scotland, which these days is a wholly distinct battle from the rest of the UK: will the SNP repeat their almost clean sweep of Scottish seats?

Note that EU referendum results weren't actually counted by constituency - the figures here are all the estimates produced by Chris Hanretty of UEA.

Conservative vs Labour battleground

This is the largest, and the real show in this election. How many seats will the Tories take off Labour, how deep into usual Labour territory will they stretch?

There are forty-two Con-Lab seats that would fall on a uniform swing of five points (including Copeland which the Tories have gained in a by-election already), eighty-two that would fall on a swing of ten points. To explain that to those who I know find talk of swings at elections baffling - a swing of 5 points is the equivalent of one party going down five points and another going up, so if a party has a majority of ten percentage points, their opponent would need a swing of five points to defeat them. This means a five point swing is the equivalent of a seventeen point Tory lead in the GB polls (ten points up from 2015), a ten point swing would be a towering twenty-seven point lead in a GB poll. A victory by twenty-seven points is, of course, a fairly outlandish prospect, but in reality the swing will not be uniform. Labour will hold some seats against the tide, and the Conservatives will take some seats that needed swings beyond the national average.

Looking down the list there are a couple of inner London seats that are heavy with young professionals and voted strongly Remain... but these largely have very small majorities, so might fall to the Tories despite that. There are also those seats that Labour took off the Tories in 2015, largely ripe for being retaken on modest swings - places like Brentford, Chester, Dewsbury, Enfield North, Wirral West and Wolverhampton SW.

Birmingham Edgbaston, a perennial Tory target that people assume has remained Labour due to the personal popularity of Gisela Stuart is there (Stuart is not, she is stepping down)

The small number of Labour holdouts in the South outside London are almost all on the list - Hove has a majority of only 2%, though was heavily Remain. Labour's last seat in the South Hampshire conurbation - Southampton Test - falls on a four and half percent swing, as does Bristol East. Exeter would need a swing of six and half percent to fall. Luton South and Bristol South fall on seven percent swings. That leaves only Slough (a 15% Labour majority and a high BME vote that the Tories would struggle with, though Labour lose any incumbency vote from Fiona Mactaggart's retirement) and the probably impregnable 22% majority in Luton North.

Most of the list is, however, made up of seats in the suburbs and provincial towns and cities of the Midlands and North. The outskirts of the West Midlands conurbation are well represented, with seats in Dudley, Coventry, Northfield, Walsall and Wolverhampton on the theoretical target list, as is Greater Manchester, with plausible targets in Bury, Bolton and Worsley. There's another group of marginals in North-East Wales and the Wirral - Wirral South and West, Ellesmere Port, Wrexham, Delyn and Alyn & Deeside. The great Northern cities themselves aren't there - the Conservatives are not viable in Liverpool, Manchester or Sheffield; Tynemouth is the only seat on Tyneside.

Looking down the list of Labour MPs at risk there are pro and anti-Corbyn MPs in the firing line: John Woodcock who is standing but refusing to endorse Corbyn is in the 8th most vulnerable seat, Corbyn ally Cat Smith is in the 14th.

Mary Creagh and Vernon Coaker have only 6% majorities to defend, Lindsay Hoyle - a favourite to be the next Speaker if he survives - has a 9% majority in Chorley.

Conservative vs Lib Dem battleground

The expectation is that the Conservatives will win seats from Labour, but that this will be blunted to some degree by losses to the Liberal Democrats. The Lib Dems have staged a modest recovery in the national polls and a strong recovery in local by-election contests. On a straight national swing we shouldn't necessarily expect them to win anything from the Tories - the Tory vote has increased as much as the Lib Dem vote. In practice, however, I would expect the Lib Dem recovery to be concentrated in places with a history of recent Lib Dem support and places that voted against Brexit.

That said, the Liberal Democrats will have pull out some impressive swings to get more than a modest number of gains. There are only ten Conservative seats with the Lib Dems in second that have majorities under 10%, another fifteen with majorities under 20%. Few of these seats were strongly pro-Remain: Kingston & Surbiton and Twickenham voted heavily against Brexit and are high on the target list, but the Lib Dem targets in Cornwall and the South West mostly voted to Leave. All of these seats are places that had Lib Dem MPs recently, and I would expect many of those former MPs to seek a rematch - the most prominent, Vince Cable, has already confirmed he is to stand again in Twickenham.

Labour vs Lib Dem battleground

Given the catastrophic performance of the Lib Dems in Labour areas in 2015 there are actually very few Lab-Lib Dem marginals on paper. In many seats that we are used to thinking of as Labour held Lib Dem targets (Sheffield Central, say) the Lib Dems collapsed to such an extent they are no longer in second place. There are plausible places where they could come from third place to win if they do particularly well, such as Bristol West and Norwich South. While there are Leave seats on this list, the most plausible Lib Dem pick ups are the mix of inner-city and university seats that voted overwhelmingly for Remain - the sort of young, well-educated areas where the Lib Dems have traditionally excelled like Cambridge, Bermondsey and Manchester. Again, these are all seats that the Lib Dems previously held and in some cases former Lib Dem MPs will be standing again - Julian Huppert and Simon Hughes are confirmed as the candidates in their former seats.

The SNP Defence

In 2015 Scotland was a crushing victory for the SNP, sweeping almost all before them. It was an effective lesson in what happens under the First Past the Post system when a new political cleavage becomes dominant, people on one side have a clear main party to vote for and the other side is split between three different parties: the side with a united vote utterly smashes the other side.

In terms of support the SNP are in the same sort of dominant position they were in 2015 and I think we can be relatively safe in predicting another easy SNP victory. The interesting thing in terms of seats will be the behaviour of the other parties. The defence list of SNP seats is below - but don't just look at the majorities, look at the shares too. For example, in both Dumfries & Galloway and Paisley & Renfrewshire North the SNP has a majority of 12%. However, in Paisley that represented an overall majority of the vote, in Dumfries the SNP vote was ten points lower, but the Unionist vote was split.

The SNP will almost certainly win the vast majority of seats, but whether they manage another almost clean sweep depends on if the Unionist vote remains split, or whether Unionist voters vote tactically for the party best placed to beat the SNP. Since 2015 the Scottish Parliament elections and the subsequent polls suggest that the Scottish Tories have sneaked past Labour to become the most popular Unionist party in Scotland... whether Scottish Labour voters are willing to vote tactically for a Tory is an interesting question.

Other interesting seats

Besides those main battlegrounds there are, as always, various other seats that are interesting in their own unique ways and worth keeping an eye on:

• Thurrock was an extremely tight three way marginal between UKIP, Conservative and Labour in 2015. If the UKIP vote collapses towards the Tories it should be safe for them.
• Richmond Park was a Conservative seat in 2015 but has already been won by the Lib Dems on a huge swing after Zac Goldsmith's resignation. Can they retain it without the focus of a by-election and a proper Conservative candidate against them?
• Brighton Pavilion is currently the Green party's sole seat - with Labour in retreat they should hold it.
• Bristol West and Sheffield Central both have the Green party in second place. In Bristol the Greens are very clearly the main challenger, 5000 ahead of the Lib Dems in third place. Sheffield Central meanwhile is a very pro-Remain university seat where the Lib Dems have traditionally done very well.
• Manchester Gorton was due to have had a by-election, cancelled because it was overtaken by the general election. The Lib Dems were reporting a strong performance there and they will, of course, already have done a lot of leafletting and campaigning there.
• Ynys Mon and Edinburgh South are the two Labour seats at most risk to Nationalist candidates - Plaid in Ynys Mon and the SNP in Edinburgh South, their sole remaining Scottish seat
• In Southport the incumbent Liberal Democrat MP John Pugh is standing down. Given their reliance upon the personal vote of their Members of Parliament the Lib Dems have sometimes struggled to pass on seats when an MP retires (though they have done so in Southport before, retaining the seat when Ronnie Fearn stepped down in 2001)
• Orkney and Shetland is the Lib Dems sole seat in Scotland, a Liberal seat since 1950. Alistair Carmichael survived a failed legal challenge to his election in 2015, concluding that he had not committed any illegal practice, but that he had lied. Whether that saga has any impact on Carmichael's support remains to be seen.
• Finally there is Clacton, UKIP's sole constituency at the 2015 general election. It was held by Douglas Carswell at a by-election when he defected from the Conservatives and again at the general election. Carswell himself has since left UKIP and endorsed the Conservatives at the next general election, though will not stand himself. That may mean it is an easy Conservative gain, though Arron Banks is still to confirm whether or not he will go through with his intention to stand there now Carswell has stepped down.