Labour has more than halved the Conservatives' lead in the polls as it enjoys a boost on the back of its party conference.
A YouGov/Sky News poll released last night put the Tories on 37 per cent, down three since Friday, with Labour rising six points to 30 per cent and the Liberal Democrats unchanged on 21 per cent. If replicated at the next general election, the figures would result in a hung parliament.
It is traditional for all parties to receive a boost in the polls during their conferences thanks to greater media exposure. But ministers will see the increase in support as a sign that significant sections of the public remain receptive to Labour's message.
The poll raised the spirits of delegates angered by the decision of the Sun to abandon Labour after 12 years of support and back the Conservatives.
The trade union leader Tony Woodley received a standing ovation from party members yesterday after he tore up a copy of the paper on the conference platform.
Woodley, the joint general secretary of Unite, urged Britain to follow the example of Liverpool where thousands of readers boycotted the paper after it blamed fans for the Hillsborough football stadium disaster.
"We do not need an Australian/American coming to our country with a paper that has never supported one progressive policy and telling us how politics should be run in this country," he told the conference in Brighton.
As he shredded the paper owned by Rupert Murdoch, he added: "In Liverpool we learnt a long time ago what to do. I just wish the rest of the country would do the same thing."
Harriet Harman will close the conference today with a speech insisting that Labour can still beat the Tories.
The party's deputy leader launched an outspoken attack on the Sun yesterday and declared that Labour would not be "bullied" by the tabloid.
She said: "I am speaking to you this morning about something the Sun knows absolutely nothing about: equality," she told the party conference.
"The nearest their political analysis gets to women's rights is Page 3's News in Briefs.
"We are all angry about the Sun this morning, but I say to you: don't get bitter, get better. Don't get outraged, get out there. Don't get mad, get mobilised.
"Yes, we may be the underdog, but we will not be bullied. This underdog is biting back."
In a series of broadcast interviews yesterday morning, Gordon Brown sought to downplay the paper's decision to support David Cameron and said that readers wanted news "not propaganda."
"It's the British people that decide elections. It's the British people that I'm interested in and it's the British people that I was talking about yesterday," he told GMTV.
"I think that Sun readers actually, when they look at what I said, will agree with what I said.
"Newspapers are entitled to their opinions. Obviously you want newspapers to be for you. But I've got an old-fashioned view. You look to newspapers for news, not propaganda. I don't think editorials will decide elections."