There is "nothing patriotic" about backing a Brexit and "turning a blind eye to credible warnings of economic disaster", Alistair Darling will say today.
The former Labour chancellor will also warn "dark clouds are gathering on our horizon" and compare uncertainty around the EU referendum with the period before the 2008 financial crisis.
In a speech today for Britain Stronger in Europe, Darling will condemn the campaign for Brexit, saying they "can't guarantee trade without tariffs, which would push prices up. They can’t guarantee investors won’t leave Britain, risking jobs. They can’t guarantee our service sector will have free access to Europe, hitting growth."
He will say that voting to leave the EU "is simply not a risk worth taking".
Darling will also highlight new research out today, from London First and Frontier Economics, claiming that if the UK followed the Canadian trade model, “as Vote Leave has advocated”, trade could fall by £92bn.
Darling will say: “There is nothing patriotic about turning a blind eye to credible warnings of economic disaster, just as there is nothing patriotic about saying we are unable to hack it in a club that is big enough for 27 others, but not the United Kingdom."
Comparing the current situation to his experience around the financial crash of 2008, Darling will say: "The single most important determinant of the health of our economy is confidence, and it is waning as the risk of leaving comes in to focus."
He will add: "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.
"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.
"We can’t afford to take a decision where no one on the other side has any clear idea of where we would end up if we left."