THERESA May is under pressure from the EU, the Irish, the Northern Irish and many of her own party members to spell exactly what it is she wants to see happen in Ireland after Brexit.

The Prime Minister is due today to set out the UK’s response to the EU’s draft withdrawal treaty and flesh out why she wants England, Scotland, Wales and Northern Ireland to go it alone out of the single market and customs union.

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Her critics have insisted she can’t quit the bloc, and not have a hard border on the island of Ireland.

However, May and her ministers say they can, but they’ve not yet quite fully explained how.

The Tory government believes technology and new IT systems could avoid the need for an actual physical border checks.

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Though, they’ve yet to tell the EU or the Irish what technology they would use, or how this might work, and Brussels is a little sceptical.

The EU’s draft treaty paper, published on Wednesday, sets out three possibilities for Ireland.

Firstly, there’s the agreeing of a deep free-trade agreement with the UK which means some regulatory alignment between the bloc and Britain. Then there’s the UK government’s proposed, if not fully defined, technical solution.

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As its “backstop” if no solution can be found, the EU has said they retain the option of a “common regulatory area” after Brexit, effectively keeping Ireland in the customs union.

May has said she finds that utterly unacceptable, saying it would “threaten the constitutional integrity of the UK” by creating a border down the Irish Sea.

In a speech in Brussels before travelling to London, Tusk said he was “absolutely sure that all the essential elements of the draft” would be accepted by the remaining 27 EU member states.

“Until now no one has come up with anything wiser than [the EU plan],” he said. “In a few hours I will be asking whether the UK government has a better idea that will be as effective in preventing a hard border between Ireland and Northern Ireland.”

“Everyone must be aware that the UK red lines will also determine the shape of our future relationship,” Tusk said. “I want to stress one thing clearly: there can be no frictionless trade outside the customs union and the single market. Friction is an inevitable side-effect of Brexit by nature.”

Later, as he sat alongside May in Number 10 during a photocall, Tusk told the Prime Minister: “I’m absolutely sure that after your so-called red line ... well I’m not happy with it, you know, but of course, but it’s natural that you have maybe different points of views when it comes to the essence of Brexit.

“Anyway, after your decision on no customs union and no single market it’s some kind of breakthrough and we can start our substantive negotiations immediately.”

An EU source told Sky News, that Tusk’s meeting with May was “an open and honest debate in a good atmosphere about the real political difficulties lay ahead of us”.

They said the “main focus was on the content of, and process towards, the future relationship post-Brexit” with the European Council president having taken note “of the repeatedly stated UK red lines and recalled that the red lines will shape the future relationship”.

A Downing Street spokesperson said Tusk and the Prime Minister “held a positive and constructive meeting”, where they looked forward to the European Council summit later this month.

Meanwhile, Tony Blair has become the second former Prime Minister in a week to intervene in the Brexit debate. He called on the EU to stymie Brexit.

“Some in Britain believe that therefore Europe will bend in its negotiating stance and allow Britain largely unfettered access to Europe’s single market without the necessity of abiding by Europe’s rules”, Blair told an audience in Brussels. “This won’t happen because quite simply it can’t.”

“We have months, perhaps weeks to think, plan and act”, he said. “The argument in Britain is far from over. It is in flux. See the speech of Jeremy Corbyn [endorsing a new customs union] this week.”

Meanwhile, the European commission’s vice-president, Frans Timmermans, told MEPs that it was time for those in positions of power in Britain to publicly admit the consequences that would flow from the prime minister’s red lines.

“Those who championed Brexit are also under the responsibility to explain to their constituents why this is going to be such a tremendous success,” he said. “And it is just too easy to then invent a situation as if we were there to punish them. It is not our fault that things are not working out.”