The outcome of the EU referendum is set to be "very, very close", former chancellor Alistair Darling has warned.
Lord Darling, who headed up the campaign against Scottish independence and who is now campaigning to keep Britain in the EU, said every vote cast on June 23 would count.
"This is a very, very close vote. No one can predict with any certainty what is likely to happen," he told a Britain Stronger In Europe event in London.
"I hope we will win and I hope we will win well but we need to get the support of people the length and breadth of the country, no matter what there political allegiance has been in the past.
"We need every single vote. It is going to be very close. Every vote counts."
Lord Darling acknowledged that the issue of immigration from the EU was a "very big concern" for voters across the country.
But at the same time he highlighted reports warning that Britain will need to keep up the numbers coming into the country if it is avoid another economic downturn.
"Many studies show the only way of reducing the risk is to continue with current levels of immigration from the European Union - the very thing the Leave campaigns have set themselves against," he said.
Lord Darling drew on his experience at the Treasury at the time of the 2008 crash to underline the economic dangers of uncertainty surrounding Brexit at a time when "dark clouds" were gathering on the economic horizon.
After the International Monetary Fund warned that a Leave vote could wreak "severe" damage to the UK economy and beyond, he said there was "nothing patriotic about turning a blind eye to credible warnings of economic disaster".
"We know what happens when confidence plummets. We saw that in 2008 and we are still living with the consequences of the global financial crash," he said.
"Confidence remains low and uncertainty is making that worse. When the IMF single us out as facing what will be a self-inflicted wound, we can't ignore it."
He pointed to the costs of leaving the single market and doubts surrounding the sort of trade deal Britain would be able to negotiate from outside the EU.
He highlighted new research by former cabinet secretary Lord O'Donnell's Frontier Economics consultancy suggesting that Britain could lose £92 billion in overall trade if it adopted the "Canadian model" as some Leave campaigners have advocated.
"They are offering a fantasy future where we keep all the benefits of being in Europe without being part of the single market. It's Project Fantasy," he said.
"As a country whose long-term economic recovery relies on the health of our exports and our regulatory environment being attractive to global investors, it would be a colossal surrender of power to walk away from our largest trading partner, increase uncertainty, erect trade barriers and diminish our influence."
His comments were dismissed by Ukip leader Nigel Farage, who said: "It is remarkable for somebody who is supposed to be intelligent that he can stand up and say that if we weren't members of a political union we couldn't buy and sell goods to and from each other - quite extraordinary.
"China sells 300 billion worth of goods to the EU. America sells 200 billion worth of goods to the EU every year, and they haven't even got a trade deal at all."