Voters support the idea of holding a second EU referendum by a 16-point margin, according to one of the largest opinion polls in the UK since the Brexit vote.
The ICM survey, conducted as part of a Guardian reporting project, found 47 per cent of people would favour having a final say on Brexit once the terms of the UK's departure are known, while 34 per cent oppose reopening the question.
Excluding the roughly one-fifth who do not have a view gives a lead of 58 per cent to 42 per cent for a second referendum, showing rising interest in the idea as concern grows over the direction of recent negotiations.
The increased backing has come from both sides of the debate, with one-quarter of leave voters in favour of having another referendum on the final deal.
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Mounting concern about the impact of leaving, with 43 per cent of voters worried Brexit will have a negative effect on the UK economy and a narrow majority believing it will have a negative impact on the “British way of life”.
Signs that Labour voters may be becoming more open to a rethink, with 9 per cent of the party's leave backers switching to remain, and stronger support for a second referendum in marginal Labour seats than elsewhere.
A hardening of the Brexit demographic divide, with young voters 17 per cent more likely than before to support remain and over-65s more determined than ever to leave.
A widening of the geographic gulf, with voters in Scotland even more likely to vote remain, but support for leave holding up in Wales and parts of England, such as the Midlands.
The consequences of revisiting the vote are hard to predict, with the country still split largely in two, and signs of both camps hardening their positions.
The poll was underpinned by Guardian journalists reporting from around the country, where they found support for leave hardening in Mansfield, Labour supporters arguing for a second referendum in Bristol, older voters in Torbay who continue to wholeheartedly back Brexit, and students in Leeds angry and concerned that it is going ahead.
Overall, the ICM poll, carried out in mid-January, confirms a small but persistent shift in recent months towards remain, with 51 per cent of those expressing a view saying they were now in favour of staying in the EU.
But this would be a tighter margin than the 52 per cent leave result of the June 2016 referendum, suggesting a clearer mandate for reversing the decision would only come if growing numbers of leavers reacted negatively to the conclusion of negotiations with the EU.
Pollsters have struggled in recent years to predict correct outcomes, although the 5,075 people polled is a representative sample five times bigger than many similar surveys.
Alex Turk, a senior research executive at ICM Unlimited, said: “On the results of this poll of 5,000, the result of a second EU referendum would be far from a foregone conclusion.”
To the extent that there is a shift towards remain, it is largely due to voters who did not, or could not, participate in the referendum saying they would be more likely to do so next time. Of those who voted, 90 per cent said they would stick to their previous choice, and the numbers of people switching sides largely cancel each other out.
Growing EU support in both camps
But it is the growing numbers of people in both camps who favour revisiting the question that is likely to have the biggest short-term political impact.
Previously, support for a second referendum had been limited. A smaller Guardian/ICM poll in December found 45 per cent of voters wanted the UK to leave the EU regardless of the outcome of negotiations, with 32 per cent wanting a second referendum and 10 per cent favouring a parliamentary vote.
What would happen if parliament were to reject the Brexit deal remains unclear, but many pro-EU campaigners increasingly argue that a vote could be phrased in such a way as to give Britons a chance to change their minds about the overall departure from the EU if they did not like the terms on offer.
Representatives from several leading pro-EU groups met in London recently to consider ways of working more closely on overturning Brexit, rather than merely campaigning for a less extreme version, a tactic some senior business leaders are privately known to favour.
Support for asking the question is also growing in unlikely quarters, as the weakness of the government’s mandate and negotiating stance becomes clearer.
Speaking earlier this month, the ex-Ukip leader Nigel Farage said: "Maybe, just maybe, I'm reaching the point of thinking that we should have a second referendum on EU membership."
On Wednesday, the Conservative MP Jacob Rees-Mogg criticised the Brexit secretary, David Davis, for proposing a two-year transition that would leave Britain as a “vassal state” and pointed out that it would soon have less influence.
Donald Tusk, the European council president, has said the EU would be open to a British rethink, while a group of former German business leaders has called on Brussels negotiators to offer a compromise deal on immigration that would help persuade the UK to reverse Brexit.
The ICM poll found 32 per cent thought Brexit would have a positive impact on the UK economy, compared with a 38 per cent response when the same question was asked last February.–Guardian