With Brexit still unresolved, and smaller parties hoping to break through, pollsters and pundits have warned that this general election is the most unpredictable in decades. Here are five factors that could make the difference:
1) Is it all about Brexit?
Labour has settled its Brexit policy, and will hope to stand out as the one party offering to “let the people decide” by offering a referendum within six months of taking office.
But Jeremy Corbyn knows that will not be enough for many ardent remainers in his own party, and among its voters, who believe, as his deputy Tom Watson put it in a speech earlier this year, “our members are remain, our values are remain, our hearts are remain”.
If remain voters feel more motivated by stopping Brexit than any other issue, they may feel tempted to opt for Jo Swinson’s “bollocks to Brexit” Liberal Democrats.
Corbyn will therefore hope to recast the campaign away from Brexit, towards Labour’s “transformative” domestic agenda, including wholesale renationalisation, radical labour market reforms and a dramatic increase in public investment.
2) Is the big squeeze on, or can smaller parties flourish?
In 2017, the Lib Dems had hoped to rally disgruntled remainers to their cause – and the party’s then leader Tim Farron even suggested they could “do a Trudeau”, and overhaul the official opposition.
But as the gruelling seven-week campaign went on, Farron got tangled up in questions of sin and sexuality; while voters appeared to have decided their choice was about which party would be in government – and that meant Labour or the Tories.
In the event, despite portentous predictions about the end of two-party politics, Labour and the Conservatives scooped up 82.4% of the vote between them – the highest score for the two main parties since 1970.
Swinson is already pressing to be included in TV debates as she attempts to break in on that duopoly, and her supporters hope the electorate will warm to her.
And Boris Johnson’s fate will also depend on how successful the Brexit party can be in scooping up disgruntled leavers – and how aggressive its leader, Nigel Farage, will be in pursuing the PM for failing to meet his “do or die” pledge of leaving on 31 October.
3) How will the leaders perform on the campaign trail?
Corbyn’s uplifting rallies and Theresa May’s stilted stump speeches helped turn around voters’ perceptions of the two leaders in 2017.
Johnson’s team, many of whom are Vote Leave veterans, are convinced he can recapture the rough-and-tumble of the 2016 referendum campaign, which saw him outshine David Cameron.
But he has sometimes appeared chaotic or undisciplined during public appearances since becoming PM – and campaigns can be unpredictable.
For Labour, meanwhile, it may be hard for Corbyn to recapture the freshness of 2017, when he was barely known to many voters, and before he became sucked into the mire of Brexit in parliament.
And while his poll ratings as a leader were poor back then – and improved during the campaign – they are now even worse. Ipsos Mori says he has the lowest leadership satisfaction rating for any opposition leader since 1977.
4) Can Johnson do better than May at winning over Labour voters?
May’s ill-fated manifesto launch in 2017 was held in Halifax – one of a swath of Labour seats across the Midlands and Northern England they hoped to take.
In the event, May’s “strong and stable” slogan was much less successful than her boosters hoped at winning over former Labour voters: aside from a handful of seats, including Middlesbrough South and East Cleveland, and Mansfield.
However, Labour majorities were squeezed in many Brexit-voting former industrial areas, such as Gloria De Piero’s Ashfield seat, and Paul Farrelly’s in Newcastle-under-Lyme. (Both are standing down).
This time around, the Conservatives have discarded the austerity policies that have characterised their last nine years in power – and will have a manifesto aimed squarely at working-class, former Labour voters.
Johnson has been visiting a hospital or a school almost every day in recent weeks; and Tory strategists hope Priti Patel’s tough stance on law and order will help them to exploit what they regard as a weak spot for Labour, and for Corbyn in particular.
Patel, the home secretary, said at last month’s Tory conference that her party’s message to criminals was “we are coming after you” – and senior party figures were keen to tell stories of the warm welcome they were receiving on the doorsteps in Tory heartlands.
Corbyn’s fancy footwork on Brexit is partly about allowing Labour to have an offer to make to voters in seats like these – and the party also has a list of snappy retail policies, including free prescriptions and funded social care. But Johnson’s allies believe he can cut a swath through the Midlands and the North of England.
5) Where do Tory remainers go?
The departure of a string of high-profile moderates from the parliamentary Conservative party has underlined its rapid transformation in just months, during Johnson’s premiership.
Some, including Amber Rudd and Oliver Letwin, have had the whip removed, while others, including David Lidington, have announced in recent days that they are quitting parliament.
Several have voiced fears that traditional Tory voters in constituencies like theirs will have nowhere to go. Former justice secretary David Gauke, who represents South West Hertfordshire, suggested what he called Johnson’s “Farage-lite” strategy could cost his party millions of votes.
Will the fear of a leftwing Corbyn government sting longtime Conservative voters into returning to the fold? Or will they be disillusioned enough to find a home elsewhere – perhaps most likely with the Lib Dems.
Swinson told St Albans MP Anne Main – a leaver representing a remain seat – that she had already visited her constituency, and hoped to do so many more times in the weeks ahead.
Many of these commuter-belt seats will be high on the Lib Dems’ target list – and the more of them Johnson loses, the more ground he needs to make up elsewhere.
• This story was amended on 31 October. An earlier version mistakenly said that Halifax is in the north-east.
