Britain would refuse to enforce any new border in Ireland even if there is a ‘no deal’ Brexit, a Cabinet minister has told The Independent.

The minister said it would be “impossible” to put a hard border in place simply because the area needing to be enforced is too great.

With the EU saying this week that a border is the only option if Britain refuses to stay aligned with European customs and regulation, the minister added: “If they want to put up a border, let them try.”

The Cabinet minister told The Independent: “It's impossible to put a border in place between Northern Ireland and the Republic.

“You cannot put up enough fences. It was the same in the 70s – we could never stop terrorists coming across it. Even if there is no deal, I can see no reason why we would try to enforce the border.”

Theresa May’s approach to Brexit has seen her insist the UK can leave the EU and its customs union while also keeping the border in Ireland all but open – something which is seen by many as critical to peace in the region.

But earlier this week the EU’s chief Brexit negotiator Michel Barnier published a draft withdrawal agreement text, which proposes a "common regulatory area" across Ireland if other solutions to avoid a hard border fail.

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It would create a customs border in the Irish Sea unless Ms May agrees to alignment across the UK – effectively keeping the entire UK in the EU customs union and single market, which she has ruled out.

In response Ms May said in the House of Commons: “The draft legal text the Commission has published would, if implemented, undermine the United Kingdom common market and threaten the constitutional integrity of the United Kingdom by creating a custom and regulatory border down the Irish Sea.”

She added: “No United Kingdom prime minister could ever agree to it. I will be making it crystal clear to President Juncker and others that we will never do so.”

She reiterated the point to European Council President Donald Tusk after meeting him at Downing Street on Thursday.

Before Christmas, after the DUP vetoed the proposal for the customs border to be moved to the Irish Sea, the Government agreed to “full alignment” across the UK, as a “backstop” solution.

For two months, it has been pointed out that this was likely to require the UK to remain within the customs union and single market – but Ms May’s officials promised solutions that circumvented the problem would emerge.

Theresa May says 'no Prime Minister would ever agree' to EU’s proposal for Northern Ireland to remain aligned with the Republic after Brexit

The renewed row comes as Ms May puts the finishing touches to a major speech on Brexit which she is to deliver on Friday, setting out how she sees future relations with the EU developing.

She is expected to flesh out how the UK would address the Irish border questions, which goes to the heart of how Brexit will work.

After the meeting with Mr Tusk, a spokesman said: “The Prime Minister briefed the President on the speech she will deliver tomorrow on the ambitious economic partnership that she hopes to agree with the European Union. This will sit alongside the deep security partnership that she argued for in her Munich speech last month.