Mr Duncan Smith, who led the party from 2001 to 2003, has been a staunch supporter of Mr Johnson’s leadership campaign. With US President Donald Trump eyeing up a potential trade deal, Mr Duncan Smith said the former London Mayor was in an excellent position to form such a deal. He wrote in the Daily Telegraph: “His cast-iron October deadline will allow discussions with America to commence this summer.”
Mr Duncan Smith said Theresa May’s withdrawal agreement made free trade deals unlikely as despite the US administration saying they would like a deal as soon as Britain left: “The withdrawal agreement negotiated by Theresa May made that impossible because we would not have left the EU.”
He contrasted this with fellow Mr Johnson, whose leadership campaign he is chairman of: “His Brexit deadline opens the door for accelerated talks with the United States and other nations to get such a free trade done swiftly, with those discussions able to begin this summer.
“There will also be certainty to those talks, as the US will know both when we are leaving and that we intend to do so properly.
“Not just the USA, for this opens the door for accelerated talks with other allies worldwide.”
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Mr Duncan Smith called for Britain to lead “the drive for global free trade” and “regain our rightful place as a global trading nation”.
The column was concluded with a remark that: “Of course, none of this can happen unless Conservative Party members cast their votes for Boris Johnson.”
Mr Johnson will take on Jeremy Hunt in a ballot of the 160,000 Tory members.
Ballot papers have been received by members and an image posted by blog Guido Fawkes shows it says the deadline is July 22 at 5pm.
The winner is expected be announced July 24.
Mr Johnson has been the favourite with bookmakers ever since the beginning of the race.
He got around half of the votes from Tory MPs in the final parliamentary leadership ballot.
However, Mr Duncan Smith may be wary of what happened in his leadership campaign.
Michael Portillo started the campaign as favourite and initially, Mr Duncan Smith struggled to get more than 30 percent of the MP votes.
However, Mr Portillo was edged out in the final ballot by Ken Clarke and Mr Duncan Smith who ended up getting 60 percent of the membership vote.