Uxbridge & South Ruislip
Held by: Boris Johnson (Conservatives)
Majority: 5,034
Expected declaration time: 04:00
The prime minister represents Uxbridge & South Ruislip, in the outer reaches of northwest London. He won it in 2017 by a decent-sized majority of over 5,000. YouGov's highly-anticipated MRP poll, unveiled on Tuesday, put Johnson nine percentage points ahead of Labour candidate Ali Milani. Johnson will be confident of avoiding a humiliating defeat.
However, Conservative party HQ will be nervously be keeping one eye on what unfolds in this seat the early hours of Friday morning. Since YouGov published the findings of its poll, prominent Labour supporters have pointed out that the combined projected vote share of the Liberal Democrats and Green Party in this seat is, you guessed it, nine percentage points.
If the polls are right Johnson is unlikely to lose his seat, but if the exit poll shows we're heading for a hung parliament then the prime minister could have a nervous few hours waiting for the result.
Canterbury
Held by: Rosie Duffield (Labour)
Majority: 187
Expected declaration time: 04:00
Canterbury will be followed by the eyes of the nation in the early hours of Friday morning.
This cathedral city in Kent, which Business Insider visited last month, is the epicentre of a countrywide debate about whether anti-Brexit candidates should work together to stop Boris Johnson returning to Downing Street.
In this case, the Liberal Democrats have refused to stand aside for Labour's Rosie Duffield, who won the seat in 2017, despite her being a vocal supporter of a new Brexit referendum and staying in the European Union. This has left Duffield with an even bigger challenge of defeating Conservative challenger, Anna Firth, and keeping hold of the constituency.
Her majority is a very slim 187. YouGov's MRP projection suggests Duffield will hold on to the seat. Failure to do so will mean that Britain's Remain-parties are heading for a bad result.
Workington
Held by: Sue Hayman (Labour)
Majority: 3,925
Expected declaration time: 01:00
Workington, over three miles away from Westminster on the stunning but remote Cumbrian coast, has become an unlikely focal point of this general election. Conservative campaigners have coined the term "Workington Man" to describe the sort of voters they must win over to deliver a victory. These are Brexit-voting, working-class men in towns that watch rugby league.
Workington is one of several Labour-held seats which the Conservatives are targeting. The Tories believe the key to an election success lies in taking chunks from Labour's "red wall" of seats, which are mostly in the north of England and the Midlands.
Labour's Shadow Environment Secretary Sue Hayman currently controls this constituency with a majority of just less than 4,000. She told Business Insider that locals had complained about feeling patronised by the "Workington Man" label. However, she acknowledged that she had a fight on her hands keeping the seat out of Johnson's clutches.
The Conservatives have controlled Workington for just three of its 100 year history. A victory here in the early hours of Friday morning would help pave the way to a Tory majority.
Cities of London and Westminster
Held by: Conservatives
Majority: 3,148
Expected declaration time: 03:00
A big feature of the Liberal Democrats' approach to the election has been standing high-profile candidates in seats where they'll need to pull off huge swings to win. The party's best chance of this bold strategy paying off is probably in the Cities of London & Westminster, where former Labour MP and shadow minister Chuka Umunna is hoping to unseat the Conservatives.
The Liberal Democrats finished nearly 14,000 votes behind the Conservatives at the last general election. However, people here voted strongly for Remain in the 2016 referendum, and the party hopes that its anti-Brexit stance can help Umunna pull off a memorable victory.
The Cities of London & Westminster will also be a test of how successful attempts by anti-Brexit campaigns to push tactical voting have been. Umunna is urging previous Labour voters in the Cities of London & Westminster to back him in order to defeat Tory candidate, Nickie Aiken.
Last month Umunna's campaign was boosted by actor Hugh Grant, who urged pro-Remain voters to back candidates like Umunna in order to prevent the "terrifying prospect" of a Johnson victory, in an interview with Business Insider.
Esher and Walton
Held by: Domonic Raab (Conservatives)
Majority: 23,298
Expected declaration time: 03:00
One of the main battlegrounds in this election has been the trend of Conservative Remainers turning away from the party towards the Liberal Democrats.
This factor could play out in one of the biggest moments of the night in the seat of Esher and Walton in Surrey, southern England where Liberal Democrat Monica Harding is trying to unseat Foreign Secretary Dominic Raab.
Raab, who was in the race to replace Theresa May as prime minister earlier this year, won Esher and Walton with a big majority of well over 20,000 in 2017. However, Jo Swinson's Liberal Democrats believe that with the help of tactical voting from ex-Labour and Green Party supporters, this Remain-voting seat could boot out this senior government minister and elect a Lib Dem member of Parliament. The Greens have stood aside to help the effort to oust Raab.
YouGov's most recent MRP projection put the Conservatives just two percentage points ahead of the Liberal Democrats. If Raab loses his seat, it could be the big "Portillo moment" of the 2019 election.
North East Fife
Held by: Stephen Gethins (Scottish National Party)
Majority: 2
Expected declaration time: 04:00
North East Fife in Scotland is the most marginal constituency in the country.
The Scottish National Party won it by just two votes in 2017. Polls are predicting another incredibly close contest this time around, with SNP incumbent Stephen Gethins neck-and-neck with Liberal Democrat challenger, Wendy Chamberlain.
Both parties are desperate to win here.
For Nicola Sturgeon's SNP, it would be a jewel in the crown of what is expected to be another strong performance for the pro-independence party. It would be a disappointing night for Swinson's Liberal Democrats if they did not gain seats, especially after polling so strongly earlier in the year, and North East Fife is close to the top of their list of targets.
