The letter is also signed by business leaders including Tim Martin, chairman of pub chain JD Wetherspoon, John Longworth, former director-general of the British Chambers of Commerce, and the economists Roger Bootle and Prof Patrick Minford of Economists for Free Trade.
Mr Duncan Smith said: “She has got to go to Brussels and tell them ‘we have put a lot on the table and you need to move’.
“This is the moment when she needs to tell them that no deal is a real threat to them. We have to move and they have to say they are ready.”
Another former Tory minister said: “We’re at the point where we need to make a decision do we go ahead with negotiations or do we say we’re going to pull out. We haven’t got the luxury of time here.
“The best thing she could do is turn up in Brussels and tell them that we’re going to go. It would be far more effective if she just said we’re off.”
A senior Government official said Mrs May would use the dinner to urge the other leaders to “focus on the opportunities and challenges ahead and encourage them to move the conversation on to consider the future partnership”.
The official added that Mrs May believes “the talks are heading in the right direction”.
However, EU diplomats have told The Telegraph they believe there is only a “50/50 chance” of any progress being made by the European Council’s final meeting of the year in December.
The leaders’ summit will take place in the Justus Lipsius Centre in Brussels after the Europa Building, nicknamed the “space egg”, was evacuated for the second time in five days yesterday.
One EU official said it meant the leaders would be served a cold supper, adding: “The dinner isn’t expected to last very long or be a very relaxed affair. The other leaders aren’t going to be in the mood to listen to Mrs May speak for too long.”
October 18th, 2017: Telegraph