UK election: An hour-by-hour armchair guide to the results

10pm: Polling stations closed across Britain and Northern Ireland. The results of a BBC/ITV/Sky exit poll were announced simultaneously on all three channels. The exit poll put the Conservatives well ahead on 316 seats, with Labour on 239 seats, the Liberal Democrats on 10, the SNP on 58 and UKIP on two as counting begins across the country. The poll predicted the SNP would win 58 of Scotland's 59 seats.

11pm: Labour wins the first seat to declare in the 2015 general election with an increased majority. Bridget Phillipson holds Houghton and Sunderland South, polling 21,218 votes, up 4.7% on her 2010 figure. Ukip's Richard Elvin polled 8,280, pushing Conservatives candidate Stewart Hay into third place with 7,105 votes. Ms Phillipson said voters "have put their faith in Labour's belief that Britain only succeeds when working people succeed too. The Tories have failed people here and across Britain."

Midnight: London mayor Boris Johnson, arriving for his count in Uxbridge and South Ruislip, said that if the exit poll was right, "then obviously, it's a very, very clear victory for the Conservatives and a very bad night for Labour".

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David Cameron leaves after casting his vote in the UK general elections at Spelsbury Memorial Hallin Witney. Photograph: Stefan Rousseau/PA Wire

SNP sources, though, said they’re confident of taking Dumfriesshire, Clydesdale and Tweeddale, the Conservatives’ only seat in Scotland. Other sources said SNP is narrowly ahead in Renfrewshire East, the seat currently held by Scottish Labour leader Jim Murphy.

Shadow chancellor Ed Balls tried to put a brave face on exit poll, telling BBC that even if it is right, Conservative/Liberal Democrat coalition majority has gone from 72 to zero and David Cameron’s ability to hang on in Downing Street is “on a knife-edge”, needing support from the Ulster unionists.

1am: After a brief lull, results are expected from some key constituencies. The result from Nuneaton, which Labour is aiming to take from the Conservatives, will give the first indication of what Ed Miliband's party is in for. The first Northern Ireland seat to be filled will be North Antrim, where the DUP's vote could offer a hint of the swing in more closely fought constituencies. That will be followed by Lagan Valley (DUP), Upper Bann (DUP) and West Tyrone (Sinn Féin) – none of which is likely to change hands.

Also expected in this hour are the first seats from Scotland and Wales. Welsh nationalist party, Plaid Cymru, will find out if it has won Anglesea/ Ynys Môn, a key target that could go its way if Ukip takes a big bite out of Labour’s vote.

2am: By now the declarations will be cascading thick and fast. The scale of the SNP's advance will become apparent with results from Paisley and Renfrewshire South, where Labour's Douglas Alexander hopes to hang on, and Gordon Brown's old seat, Kirkcaldy and Cowdenbeath. All four Belfast constituencies will declare: the one to watch is East Belfast, where the DUP is aiming to unseat Naomi Long of the Alliance Party.

Also expected around 2am is the first London declaration, in Conservative-held Battersea. Even more important for David Cameron’s party is Bolton West, its second target seat. A loss there would be a huge setback. Ukip supporters will be keeping a close eye on the first declarations from Essex and Lincolnshire, where the party has a number of Tory-held targets.

3am: A critical hour, with results that will tell us a great deal about the shape of the next parliament. Labour's leader in Scotland, Jim Murphy, will find out if he has won his battle to hold East Renfrewshire. If he is unseated, Labour's worst fears about the SNP surge will be confirmed. In England, the Conservatives will learn whether their small opinion poll leads in places such as Swindon South, Croydon Central and Lincoln were borne out in the ballot box. Lose them and the party is in trouble. Similarly, if Labour fails to take seats such as Hampstead and Kilburn, Enfield North and Bury North from the Tories, their chances of forming a government will diminish sharply.

First real indications of the Liberal Democrats’ performance will emerge with results from the party’s traditional stronghold in the West Country.

4am: All eyes – or all eyes still open at this hour – turn to Sheffield Hallam, where a defeat for Lib Dem leader Nick Clegg would traumatise the party, deprive Cameron of his preferred coalition partner, and provide one of the lasting images of the election. The Lib Dems will also find out whether their cabinet minister, Danny Alexander, and former leader Charles Kennedy have managed to hold off the SNP and retain their Scottish seats.

Elsewhere, David Cameron (Witney), Ed Miliband (Doncaster North) and Alex Salmond (Gordon) will all be declared elected.

5am: Sunrise in London, but much of the attention will be on southwest England, where at 5.30am we will have a string of results from tight contests between the Conservatives and Lib Dems. These will have a significant bearing on the size of the Lib Dem parliamentary party and on whether the Tories return to Westminster as the largest party. Labour have their eye on Margaret Thatcher's old constituency, Finchley & Golders Green, where polls show a dead heat.

In Northern Ireland, we’ll have a result from bitterly- contested Fermanagh-South Tyrone, which produced the narrowest winning margin of any Westminster seat in 2010 when Sinn Féin’s Michelle Gildernew won by a mere four votes. Will she hold on to it, or could the DUP-Ulster Unionist Party pact allow Tom Elliott take it for the UUP?

6am: Ukip's Nigel Farage said he would step down as party leader if he failed to win a seat in Thanet South, a coastal constituency in the southeast. A defeat would be a huge blow to the party. Farage will have to wait until 6am, when this three-way marginal declares, to learn his fate. Elsewhere, the Green Party's Caroline Lucas will find out if she has managed to retain Brighton Pavilion. Boris Johnson, the favourite to replace Cameron if the Tory leader resigns or is pushed, will be elected in Uxbridge and Ruislip South.

By now it will be clear which party will be the largest at Westminster. But if the result is as close as opinion polls suggest, the shape of the next government could be as unclear as it was before a single vote was counted.