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Brexiteer Tory Iain Duncan Smith was mocked by the former head of the WTO who mimed a unicorn behind his back in response to claims the Irish border issue could be solved using technology.

Pascal Lamy accused the former Tory leader of "total confusion" over alternative plans for the Irish border.

Mr Lamy said that the ardent Brexiteer was guilty of “pie in the sky” thinking.

Mr Duncan Smith claimed that if the UK would “agree to alternative arrangements on the Irish border” that there would be “no fixed border” in Ireland.

"If you want to diverge you have to accept that there will be a border," he said.

Mr Lamy was the Director-General of the World Trade Organization until 1 September 2013 but he also served as the Chief of staff for the President of the European Commission Jacques Delors.

Early today Mr Lamy blamed the Brexit impasse on Theresa May "rushing in" to discussions on the terms of the UK's divorce from the EU rather than insisting that they should take place in parallel with trade talks which will take "years and years".

He told BBC Radio 4's Today programme: "My view is that we may have made the wrong choice in deciding that we would negotiate first the Withdrawal Agreement - which is a sort of divorce agreement - and then the rest."

Mrs May's Government initially argued that the issues of withdrawal and future relations should be negotiated together, but swiftly folded in 2016 as Brussels insisted the divorce must be settled first.

"She was in a hurry, she was under huge pressure from Boris Johnson, Brexiters and the rest and she said 'Brexit is Brexit, we will Brexit' and they rushed into this first stage without understanding that this huge unclarity on the next stage would have a big bearing on the discussion," said Mr Lamy.

(Image: PA)

"I know full well from experience that negotiating a trade agreement takes years and years, so I understand why they couldn't wait for that in order to Brexit for those of the British public who wanted to Brexit rapidly."

It was now time for the EU to offer "clarity" on future relations to allay the fears of both Brexiters and Remainers that the UK will be "cheated", he said.

Both sides should seek a "totally open trade relationship", retaining as much as possible of current arrangements, said Mr Lamy, who led the WTO from 2005-13.