Here’s my complete guide to the seats I think will most shape the result of the election, and from which we’ll best judge the success and failure of all the main parties.
There are 50 constituencies in all. They include the seats I’ve already profiled for Labour, the Tories, the Liberal Democrats and some of the smaller parties, plus a few bellwethers and a handful of other contests, including some in Northern Ireland.
I’ve grouped them by region, which will hopefully make this list more user-friendly.
I’ll return to this list nearer the election and make predictions for the result in every seat.
The 50 key seats
If John Thurso loses in here, things will be looking grim for the Lib Dems’ 11 Scottish MPs. In 2010 Thurso managed a majority of 4,826 over Labour, with the SNP coming third. The nationalists need a swing of 11.1% to win.
If the SNP takes this seat, they will have managed a swing of 24.9% and the Labour party’s days as a dominant force in Scottish politics will truly be over. A poll published in February by Lord Ashcroft put the SNP three points ahead.
The Tories’ only seat in Scotland. It’s notionally a Labour target, with the party needing a swing of 4.6% to take the constituency. But the SNP will fancy their chances here, despite needing a 13.6% swing for victory. If the anti-Tory vote ends up being split three ways, David Mundell could well hold his seat.
A test of how well Labour deals with the challenge of the SNP. Jim McGovern has a majority of 7,278: the kind that in previous elections would have been described as safe. A swing to the SNP of 9.8% would be needed for him to lose. The constituency next door, Dundee East, is an SNP stronghold.
This is a potential five-way battle between Labour, the SNP, the Liberal Democrats, the Tories and the Greens, and as such will be one most intriguing contests in all of Scotland. The Greens polled 5.1% in 2010. The SNP polled 20.4%, and need a 11.5% swing to take the seat. Just how will the anti-Tory/left-wing vote split?
The SNP needs a whopping 18.4% swing to win. A change of party would signal an almighty electoral earthquake was under way in Scotland.
The Lib Dems’ Malcolm Bruce is stepping down from this seat after 32 years. Christine Jardine is hoping to succeed him, and only one person stands in her way. Unfortunately for Jardine, that person is Alex Salmond, who needs a 6.9% swing to take the seat.
A juicy target for the SNP, for if they win it from the Lib Dems, they’ll not only have managed a swing of 11% but unseated the chief secretary to the treasury Danny Alexander. A total of three Lib Dem seats would fall to the SNP on a swing of this size – but another three would change hands if the nationalists manage to push the swing one point higher to 12%.
The SNP’s “easiest” gain from Labour, but I’m using inverted commas because a swing of 5.2% is by no means easy. I expect the party to manage it, but the real test will be whether they manage it by some margin, or whether the result is close.
Labour held Carlisle continuously from 1964 until 2010, when John Stevenson won the seat for the Tories. Stevenson’s majority is only 853 and a swing of 1% would send the constituency back into Labour’s column. It’s the type of seat Ed Miliband needs to win by a decent margin if he is serious about getting into Downing Street.
Can Ukip do what it almost managed to do in the by-election of October 2014 and win this constituency from Labour? A swing of just 1.1% is all Ukip needs to overturn Liz McInnes’ majority of 617.
There is a prize Tory scalp for Labour in this seat: employment minister Esther McVey, who would be defeated on a swing of 3.1%. This is precisely the kind of seat Labour needs to win to be secure of ending up the largest party in parliament.
Sir Alan Beith is standing down from the seat he has held for the Liberal Democrats continuously since 1973. The Conservatives need a swing of 3.5% for a victory. It’s the kind of seat they need to take to ensure they remain the largest party in the Commons.
Oliver Coppard is the man who hopes to defeat Nick Clegg. If he succeeds, it could be the most spectacular result of election night. But he’ll need a mammoth swing of 18.7%, and has to leapfrog the Tories who came second in 2010.
James Wharton won this seat in 2010 with a majority of only 332. A swing of just 0.3% would deliver it back into the hands of Labour. If Ed Miliband can’t rely on taking constituencies like these, he has no hope of outperforming the Conservatives.
This is often spoke of as Ukip’s best chance of a gain at the general election. The party managed a 9.5% share here in 2010, and needs a gigantic 20% swing to win the seat from the Conservatives. The sitting MP Mark Simmonds is standing down, and an opinion poll commissioned by Ukip in September 2014 placed the party 20 points ahead of the Tories.
Austin Mitchell is standing down here as Labour MP after 37 years. In 2010 he had a majority of just 714, and the seat is a top target for both the Tories and Ukip. Whether Mitchell’s successor Melanie Onn can see off both threats will be a key marker of how Labour is performing in its most marginal constituencies.
Chloe Smith won this seat from Labour on a huge 16.5% swing at a by-election in the dying days of Gordon Brown’s government. She held the seat in 2010 but with a reduced majority, and Labour now needs a swing of 4.6% to take it back. If it succeeds, the party could be heading for at least 300 MPs in parliament and even a slender majority.
Plaid Cymru gained this seat from Labour’s Alan Pugh in 2010. Now Pugh is attempting to take it back. He needs a swing of 2.8% to do it, and whether he succeeds will be a good indication of how Labour is faring against the Welsh nationalist vote.
Plaid may be able to take revenge for losing Arfon by gaining this seat from Labour. They need a 3.6% to win it, however, and will be hoping to profit from a collapse in the Labour vote similar to the one towards the SNP in Scotland.
This will be a test of how well Labour is doing in picking off its Lib Dem targets. John Hemming achieved a majority of 3,002 in 2010, and the seat would change hands on a swing of 3.7%. If Birmingham Yardley remains out of Labour’s grasp, Ed Miliband will have failed to make the kind of advance into Lib Dem seats that he needs to offset potential losses elsewhere.
Chris Williamson has a majority of only 613. If Ukip-inclined supporters vote tactically, and if the left-wing vote is split, the Conservatives may end up winning the seat. It’s the sort of scenario the Tories will be relying on to chip away at Labour’s overall tally of constituencies.
Ian Austin’s majority of 649 makes him vulnerable to a Tory swing of just 0.9%. Ukip are also targeting the seat, though their intervention may simply tip the balance back towards Labour.
If Labour wins here, it will have achieved the sort of swing (3.5%) needed to become safely the largest party in parliament. This is also the seat of education secretary Nicky Morgan, so there’s the added attraction of defeating a high-profile member of the cabinet. Loughborough has been a bellwether seat in general elections since February 1974.
Another bellwether seat. Since its creation in 1974 its voters have always elected an MP from the party that has gone on to win the general election. Labour needs a swing of 2.4% to defeat the sitting MP Michael Ellis.
Labour held this seat from 1992-2010, and before then from 1935 all the way through to 1983. It needs a 2.3% swing to win it back from the Tory MP Marcus Jones, but if the party only just scrapes victory, it will suggest a very patchy performance across the country.
This is the Liberal Democrats’ most marginal constituency in the country. Lorely Burt is defending a majority of just 175, and the Tories need a swing of 0.2% to gain the seat. It should change hands easily, but it will be the size of the Conservatives’ victory that will be worth watching.
Can the Greens double their representation in the Commons from one to two MPs? Bristol West is the party’s top target, but candidate Darren Hall would need a swing of 22.1% to win, and this Lib Dem-held seat is also being eyed by Labour and the Tories. The Greens polled 3.8% here in 2010, and believe they will do better this time thanks to both the Lib Dem and Labour vote collapsing in their favour.
Dan Rogerson’s majority is only 2,981, but the Tories need a 3.2% swing to defeat him. If they manage it, the Liberal Democrats could be looking at losing around a third of their MPs.
Tory MP Nicola Blackwood has a majority of only 176 in this seat, and though I don’t think she’s in any danger of losing the seat, it’ll be worth watching to see how she does this time. If it’s another narrow result, it’ll be clear the Tories aren’t doing as well as they hoped in former Lib Dem strongholds.
One of the few Tory seats in southern England that Labour has a good chance of taking. Oliver Colville would lose on a swing of just 1.3%.
John Denham held this seat in 2010 with a majority of just 192. He’s standing down this year, leaving the job of defending his wisp of lead to Rowenna Davis. The Conservatives need a swing of just 0.2% to take the seat. Such an outcome would suggest the Tories could be in for a good election, quite possibly ending up once again the largest party in a hung parliament.
The sort of seat that Labour has to take if it is serious about winning the election persuasively. A 3.8% swing would see the constituency change hands, but the omens are not good. Labour unexpectedly went backwards at the 2014 local elections and lost seats on Swindon council to the Tories.
Watch to see how easily Tory candidate James Heappey wins this seat. He needs a swing of only 0.7% to defeat Tessa Munt. If he manages a majority of around 3,000, that will be a very good result indeed. Anything around 1,000 could mean the Tories will struggle in their quest to take up to eight Lib Dem seats across south-west England.
The oldest bellwether in the country. In every election since 1964 it has returned an MP from the same party that has gone on to form the government. A mighty 10.6% swing to Labour would see it change hands.
Labour needs a swing of only 1.9% to slip this seat from the Conservatives’ grasp. However the Greens polled 5.2% here in 2010. If they increase their share of the vote this time, sucking a sizeable chunk of support from Labour in the process, Hove could remain in Tory hands. It may turn out to be typical of a number of marginals across the country.
I’ve no doubt that Douglas Carswell will hold Clacton for Ukip. Will his fellow Tory defector Mark Reckless do the same in Rochester & Strood? Reckless’ majority is only 2,920. The Tories need a swing of 3.7% to take the seat back, and whether they manage it will be a good marker of their success in wooing back erstwhile Ukip supporters.
Nigel Farage needs a titanic swing of 21.8% to win this seat. I suspect the task may be simply too big for him, but it’s a contest worth watching to see how great a dent he can make into the Tory vote.
This is a fascinating contest that has become a three-way battle between sitting Tory MP Jackie Doyle-Price, Labour’s Polly Billington and Ukip’s Tim Aker. Doyle-Price has a majority of only 92. The seat ought to be an easy Labour gain, but Ukip think they’re in with a chance of an upset, and Doyle-Price is a sharp campaigner.
A bellwether since February 1974. Labour lost the constituency in 2010 after coming third behind the Tories and the Lib Dems. The party needs a swing of 4.1% to retake the seat.
A real Labour long shot. If Simon Hughes is defeated here, Labour will be having a bumper night at the Lib Dems’ expense. Hughes has a majority of 8,530; Labour’s candidate Neil Coyle needs a swing of 8.6% to take the seat.
Sitting MP Sarah Teather has already packed her bags, leaving her notional successor Ibrahim Taguri to defend a majority of just 1,345. A swing of 1.5% would see the seat change hands. If Labour win big here, it will be a good sign of how the party is benefiting from a collapse in support for the Lib Dems and also how well it is doing in London.
Tom Brake has held Carshalton & Wallington for the Liberal Democrats since 1997. This will be his sixth election contesting the seat. The Tories’ Matthew Maxwell Scott needs a 5.8% swing to win. If he manages it, the Tories could end up knocking out at least a dozen Lib Dems.
The Tories’ top target was won in 2010 for Labour by Glenda Jackson, with a majority of just 42 votes. Jackson is standing down this year and Tulip Siddiq will be hoping to hold the seat. The result will offer clues about how well the Tories are doing in London, in whose favour the Lib Dem vote is collapsing, and how robustly Labour is seeing off challenges from the Tories.
A good benchmark against which to judge Labour’s success at taking further seats from the Liberal Democrats. The party is expecting to vacuum up at least half a dozen Lib Dem marginals comfortably. But how will it fare in seats like this, where it needs a 6.3% swing to unseat Lynne Featherstone?
If this falls to Labour, the Tories really will be in trouble. It could also be evidence of the party doing particularly badly in London, where they stand to lose potentially up to nine seats to Labour. Wes Streeting needs a 5.8% swing to take the seat from Lee Scott.
The Tories need a swing of only 1.7% to overturn Paul Burstow’s majority of 1,608. Yet I suspect he may survive. Burstow has a very strong local following, and the Lib Dems performed well in this part of London in the local elections of May 2014. Polls have suggested he will hold on, and if he does it will be a model example of individual Lib Dem MPs bucking the nationwide trend and defying the odds.
Most of Northern Ireland’s 18 seats won’t change hands, but this is one that might. Naomi Long, the Alliance party’s only MP, has a majority of 1,533. The DUP will be hoping to retake the seat, and need a swing of 2.2% to do it.
Sinn Fein’s Gerry Kelly is making a remarkable fourth attempt to defeat the DUP’s Nigel Dodds. He needs a swing of 3.3% to do it, and it should be the close contest yet.
Last but definitely not least, the most marginal seat in the whole of the United Kingdom. Michelle Gildernew is defending a majority of just four. As yet it’s not clear precisely who will be her main opponent. In 2010 the main unionist parties threw their support behind an independent; so far no such candidate has been forthcoming.