Opinion polls failed to predict the outcome of last year's general election as they failed to question enough Conservative voters, an independent inquiry has found.
What happened?
In the run-up to May's election, the polls had consistently predicted that Labour and the Tories were running neck and neck and that Britain was likely headed for a hung parliament.
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However, the Conservatives secured an overall majority and David Cameron returned to Downing Street with enough seats to form a government.
"I remember the audible gasp in the BBC's election studio when [presenter] David Dimbleby read out the exit poll results putting the Conservatives clearly ahead," says political editor Laura Kuenssberg.
Why were they so wrong?
In essence, they surveyed the wrong people.
The sampling methods used resulted in the "systematic over-representation of Labour voters and under-representation of Conservative voters", says the inquiry.
Pollsters failed to question enough people in retirement and instead relied too heavily on politically engaged young people. "There is also some evidence that people who are harder to get in contact with tend to be more likely to vote Conservative," says Sky News.
The inquiry panel also failed to rule out the possibility of "herding", where pollsters design surveys and weight their responses in such a way that their results tally closely with those of other organisations.
Does that mean polls are a waste of time?
The inquiry's official recommendations are not due out until March, but pollsters insist they have already begun making improvements to their methods.
YouGov has proposed including a more detailed age breakdown; Ipsos Mori is considering taking account of people's past voting habits, and ComRes has developed a new weighting model.
Inquiry head Patrick Sturgis, of Southampton University, insists the polls should not be discounted. "The fact is that the polls are by far and away the best way of trying to figure out what the election result is going to be," he says.
The BBC's Laura Kuenssberg agrees. "Politics is not a precise science and predicting how people will vote will still be a worthwhile endeavour," she argues.
"Political parties, journalists and the public, of course, would be foolish to ignore them. But the memories and embarrassment for the polling industry of 2015 will take time to fade."
Exit poll result 2015: Conservative and Lib Dem majority in UK general election
07 May
The exit poll for the UK general election has given the Conservatives an unexpectedly strong lead, suggesting that they will be the biggest party by a large margin, even though they are still expected to fall short of a majority.
The Ipso Mori exit poll, commissioned by the BBC, ITV and Sky News, predicts the following breakdown of seats:
Conservative - 316
Labour - 239
SNP - 58
Lib Dem - 10
Ukip - 2
Green - 2
Plaid Cymru - 2
Politicians from all parties - except the Conservatives - were quick to pour cold water on the exit poll projection. Former Lib Dem leader Paddy Ashdown said he would "eat my hat" if the results matched the forecast, and the SNP cautioned their supporters against building up expectations.
If the exit poll does prove correct, it will mean that the current Conservative-Lib Dem coalition could command the narrowest of working majorities in the House of Commons, even with the Lib Dem's depleted seat count of ten - that is, if the Lib Dems were willing to stick with the partnership that led to their disastrous showing.
The exit poll was significantly out of line with the polling published in the last fortnight of the campaign, which suggested that the two main parties were tied.
After a fortnight in which Conservative hopes of a long-promised last-minute surge glimmered and then died, the latest opinion polls unveiled today suggest that the 2015 general election is heading for a dead heat.
Lord Ashcroft's final national poll, which was conducted yesterday and on Tuesday, has concluded with a tie: both Labour and the Conservatives were backed by 33 per cent of those asked.
Two other polls were published today. A YouGov poll in The Times had the two main parties level-pegging on 34 per cent, while an ICM poll conducted for the Guardian had Labour on 35 per cent, one point ahead of the Conservatives.
That means that of the eight opinion polls published in the past 24 hours, five have Labour and the Conservatives tied, two give Labour a one or two-point lead and one puts the Conservatives ahead by a point.
Taken as a whole, the most recent polling from each company included in the survey has the two main parties within the same narrow range: 30 to 35 per cent.
General Election 2015: the latest polls
Below is a round-up of the latest polls conducted by a range of companies, plus the BBC's blended "poll of polls":
Swipe to scroll horizontally
Row 0 - Cell 0
LAB
CON
LIB
UKP
GRN
OTR
Populus
34
34
10
13
5
4
Ipsos Mori
30
35
7
10
8
9
Opinium
33
34
9
13
6
5
YouGov
34
34
10
12
5
7
ComRes
34
35
9
12
4
6
ICM
35
34
9
11
4
5
Survation
31
31
10
16
5
6
Panelbase
33
31
8
16
5
8
TNS
33
34
7
15
5
5
Ashcroft
33
33
10
11
6
8
BBC avg
33
34
8
13
5
7
Election polls: have the Tories found their swing?
6 May
For at least a year Tory strategists have been insisting that the polls will swing their way as the general election approaches. Until now there has been very little sign of movement towards either of the main parties – only the SNP has made progress, and looks set to sweep the board in Scotland.
In the past couple of weeks, anxious Conservatives have once again been hoping that the electorate may be inching in their direction. Two polls at the end of last week gave their party a four-point lead, and several polls published since then had them in the lead - some by a substantial margin. Last week's Ashcroft national poll had them six points in front, and Ipsos Mori gave them a five-point lead on 30 April. Cameron was also deemed the winner of the BBC Question Time election special, by a six-point margin.
In recent day, however, the fickle polling data that has characterised this campaign has turned again, and the parties seems set to go into polling day neck and neck. Of the polls published in the past 24 hours, two have given the Tories a narrow lead, one has put Labour in front and two have had the parties level-pegging. The BBC "poll of polls" puts both main parties on 34 per cent of the vote.
Election polls: all square in latest polls, but Labour will be happier
22 April
A flurry of election polls published in the past few days has failed to identify a clear leader, little more than two weeks away from the general election.
Labour and the Conservatives are all but tied in the latest polls, with no more than two points separating them in the majority of surveys. Of the four opinion polls published yesterday, two had the Tories in the lead and two had Labour.
The apparent stalemate followed a week in which the advantage seemed to be with first Ed Miliband, when a run of polls showed his party opening up a lead, and then David Cameron, when the Conservatives bounced back with a six-point lead.
Election 2015: Who will win?
Of the two it will be Miliband who is happier with a tie. "Neck-and-neck is nowhere good enough if David Cameron wants to be certain of remaining in Downing Street," writes Don Brind, The Week's polling analyst. "That's because he's reliant on the Lib Dems, who are expected to lose heavily on 7 May, leaking seats pretty equally to the Tories, Labour and – north of the border – to the SNP."
Tory surge dents Labour's hopes
14 April
Labour's electoral momentum came to a shuddering halt yesterday as the latest opinion poll handed the Conservatives a commanding six-point lead with little more than three weeks to go until the general election.
At the end of last week, a flurry of polls had put Labour up to six points ahead of the Tories, and seemed to show that Ed Miliband's personal rating was also ahead of David Cameron's for the first time.
Until last week, most polls had shown the two main parties tied, or given one a narrow lead over the other.
If yesterday's Guardian/ICM poll proved correct, it ought to make the Conservatives the largest party at Westminster and put them in a strong position to form the next government.
However, The Week's polling analyst Don Brind says Labour will take some comfort from the latest poll from Lord Ashcroft, which was published this morning. It suggests that Miliband's party is performing better in marginal seats than national polling would suggest. That may allow Labour to keep its nose in front and cross the line as the largest party.
General election: latest polls give Labour a boost
10 April
A week in which Ed Miliband was accused of stabbing his brother in the back and being willing to betray his country over Trident has ended well for his party, with a series of polls putting Labour in the lead.
For most of the past few weeks, the two main parties have traded leads of one or two points, with each new poll contradicting the one that preceded it.
Today, however, three polls suggest that Labour has opened up a lead – one of three points, one of four points and one of six.
Even one of the two polls in which the Tories retain their lead suggests a shift in support towards Milliband's party. ComRes has the Conservatives down two points on 34 and Labour up one on 33.
But there are two flies in the ointment of for Labour: a YouGov poll which shows a shift from a narrow Labour lead to a narrow Tory lead – and new polling data from Scotland which suggests that the SNP is still poised to sweep the board.
Nevertheless, the apparent swing towards Miliband "means the Tories will have to issue yet another 'keep you nerve' message," says The Week's polling analyst Don Brind. "While Cameron and campaign chief Lynton Crosby will insist they can still be the biggest party, many Conservative supporters will be getting twitchy."
General election: latest polls put parties neck and neck
7 April
Last week's televised party leaders' debate appears to have ended in a confusing dead heat, in what many analysts believe will be a foretaste of what we'll wake up to on 8 May.
It remains to be seen what effect the debate will have on overall voting intentions – the polls listed in the table below were conducted before Thursday's broadcast – but snap surveys conducted immediately after the debate gave neither of the main contenders a decicisive win.
An ICM poll published in The Guardian gave Ed Miliband a narrow advantage, with 25 per cent saying he came out on top, compared with 24 per cent for Cameron. Farage was in third place with 19 per cent. ComRes declared the event a tie, with Cameron, Miliband and Farage all on 21 per cent.
YouGov identified Nicola Sturgeon as the clear winner – and the SNP leader's strong showing across a range of polls suggests that she must have won over English as well as Scottish voters.
The first polls measuring voting intention after the leaders' debate will be published this week.
Clegg's seat at risk in Sheffield, say latest polls
2 April
With the latest polls showing nothing to separate the two main parties, the result of the 2015 general election is likely to hinge on which party leader can put together the most stable coalition in the days after 7 May.
The suggestion that Nick Clegg is on course to lose his Sheffield Hallam constituency therefore has significance far beyond the Lib Dem leader's own career prospects.
"Labour are laying siege to the South Yorkshire seat knowing that, without Clegg, surviving Lib Dem MPs would be unlikely to enter another pact with Cameron’s Conservatives – in the event that the Tories come out of the 7 May election as the largest party," writes The Week's polling analyst Don Brind.
A poll conducted this week by Conservative peer Lord Ashcroft found that Labour candidate Oliver Coppard is leading Clegg by two points.
If Clegg does survive, he may owe his political skin to the Tories, according to the Financial Times.
"Polls also suggest the Conservatives are not campaigning as hard in the seat as they are elsewhere in the country," the paper says, "leading to suggestions they are deliberately giving their coalition partners an easy ride."
General election: latest polls end Miliband's 'Paxo bounce'
31 March
A four-point poll lead for Labour has evaporated as talk of a 'Paxo bounce' in the wake of Ed Miliband's interview with Jeremy Paxman appears to have been premature.
The latest polls put the parties within a whisker of each other, a little more than a month out from the general election.
A YouGuv survey for The Sunday Times had put Labour on 36 per cent of the vote, four points ahead of the Conservatives, two days ago. But the latest poll carried out by the same company for The Sun today put the two main parties on 35 points each.
Populus also gives Labour and the Conservatives an equal share of the vote, with both parties on 34 per cent.
And while Lord Ashcroft's weekly survey shows the Tories two points ahead of Labour, it suggests Ed Miliband is closing the gap on David Cameron in terms of personal popularity.
The Labour leader has consistently lagged behind Cameron, but many commentators felt he acquitted himself well with Paxman last week, while the PM failed to shine.
Latest polls: peaks and troughs for the coalition
18 March
There has been mixed polling news for the coalition partners in the past two days, with dispiriting figures from Lord Ashcroft offset by the suggestion from respected pollster Peter Kellner that the Tories and Lib Dems may garner enough votes to stay in office.
While most polls are predicting that the coalition parties will fall well short of the combined seat tally of 326 that they need to form a majority government, Kellner, the chairman of YouGov says they might just scrape home.
The Week's polls analyst Don Brind says Kellner's optimism on behalf of the coalition partners is driven by a belief that voters swing towards the government of the day as the election approaches.
YouGov even suggests that a popular Budget might produce a Tory surge may be large enough to let David Cameron head a minority government.
"George Osborne has the chance this week to assure the Conservatives of five more years in government," the polling organisation says. "If his Budget goes down well with voters, his party could gain enough extra support to govern on its own.
"Its prospects of an overall majority remain slim, but David Cameron might be able to lead a minority government for a full five-year term against a splintered opposition.
However, predictions of swelling Conservative support have consistently failed to materialise over the past six months, and Lord Ashcroft's polls of marginal constituencies suggest that the Tories may be fighting a losing battle.
While national support for Labour has ebbed slightly since last summer, the former Conservative party chairman found that Ed Miliband's party looks set to win seven of the eight key marginal targets seats he surveyed. In five of them, Labour support is higher now than it was in the summer.
Labour and Conservatives are neck and neck
13 March
It's already a truism of the 2015 general election campaign that this will be the closest race for decades, but the latest polls underline the point: Labour and the Conservatives are neck and neck.
A YouGov poll in The Sunday Times puts Labour on 33 per cent and the Conservatives one point ahead, while a poll conducted by Opinium and published in The Observer puts the two main parties on 34 points each. That's a one-point drop for Labour since the paper's last opinion poll, but not the shift in fortunes that the Conservatives have been predicting.
"While Tory strategists had been hoping that the Tories would by now be recording consistent leads over Labour," The Observer reported, "these have yet to materialise as both parties remain deadlocked in the mid to low 30s."
The Week's polling analyst Don Brind says: "With 59 days to go, and neither party managing to pull ahead, it’s little wonder that the Tories are apparently pinning their hopes on a tax giveaway Budget, and that scare stories of a Labour-SNP pact are gaining ground."
Labour back in front as Conservatives dip
6 March
It's not often that The Sun gives Ed Miliband reason to cheer, but the paper's latest poll has given Labour a narrow lead. Conducted by YouGuv, the survey put Labour on 35, the Conservatives on 31, the Lib Dems on 6, Ukip on 15 and the Greens on 8. Previous You Guv polls have shown either a tie or a slim Tory lead.
A second YouGov poll conducted for the London Evening Standard found that Londoners intend to vote overwhelmingly for Labour. The party has a 44-32 lead over the Conservatives, with the Ukip on 10, the Lib Dems on 7 and the Greens on 5.
"That said, with 62 days to go, it’s still basically neck-and-neck," says Don Brind, The Week's polling analyst. "Labour [is] likely to have a slight lead in terms of Commons seats, and the SNP [is] set to become the third largest party at Westminster
Ashcroft poll raises prospect of tie
5 March
The latest poll conducted by Conservative peer Lord Ashcroft suggests that both Labour and the Tories could end up with 272 seats after May's general election.
It also suggested that the SNP would become the third-largest party at Westminster, with 56 seats. Adding those to Labour's 272 would tip the two parties over the magical 326 mark – although it's far from clear that either party would agree to such a deal.
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