Theresa May was preparing to warn the EU that she would not sign up to “anything that threatens the constitutional integrity of the UK” as Boris Johnson was accused of hinting that a hard border could be reintroduced in Ireland.

A senior government source told of the prime minister’s intentions after reports that a legal document, to be finalised on Tuesday by the European commission, would include a last resort scenario under which Belfast remained aligned with European single market rules.

That suggestion would pile pressure on the relationship between the Conservative government and the DUP – on which it relies for votes in parliament – as it could pave the way for new regulatory barriers between Northern Ireland and the rest of the UK.

“This is a draft negotiating position by the EU and not a final, binding text,” said a senior government source. “We are fully committed to implementing the December agreement, but the EU should be absolutely clear that the prime minister is not going to sign up to anything that threatens the constitutional integrity of the UK or its common market.”

Quick guide Why is the Irish border a stumbling block for Brexit? Show Hide Counties and customs Inside the EU, both Ireland and Northern Ireland are part of the single market and customs union so share the same regulations and standards, allowing a soft or invisible border between the two.

Britain’s exit from the EU – taking Northern Ireland with it – risks a return to a hard or policed border. The only way to avoid this post-Brexit is for regulations on both sides to remain more or less the same in key areas including food, animal welfare, medicines and product safety. The 'backstop' in Theresa May's Withdrawal Agreement was intended to address this - stating that if no future trade agreement could be reached between the EU and the UK, then rules and regulations would stay as they are. This has been rejected by Brexit supporters as a 'trap' to keep the UK in the EU's customs union, which would prevent the UK striking its own independent trade deals. There are an estimated 72m road vehicle crossings a year between Northern Ireland and the Republic of Ireland, and about 14% of those crossings are consignments of goods, some of which may cross the border several times before they reach a consumer. Brexit supporters say this can be managed by doing checks on goods away from the border, but critics say it will be difficult to police this without any physical infrastructure like border posts or cameras, which could raise tensions in the divided communities of Ireland.

Interactive: A typical hour in the life of the Irish border Photograph: Design Pics Inc/Design Pics RF

Sources pointed out that the prime minister had made clear in December when the government published a joint report with the commission on the withdrawal agreement that its commitment to no hard border in Ireland included that there would be no divide in the Irish Sea.

The potential row came as a leaked document revealed that Boris Johnson had suggested that the government’s task was not to maintain “no border” in Ireland, but to prevent it from “becoming significantly harder”.

The foreign secretary submitted a document to the prime minister outlining how he believed the border question could be dealt with. His paper, obtained by Sky News, raised alarm bells by suggesting that even if there were a hard border, it would still allow 95% of goods to pass through unchecked.

A spokesman for the foreign secretary said the paper was designed to suggest how a “highly facilitated border” could work to help make a success of Brexit.



“The letter points out there is a border now and the task the committee face is stopping this becoming significantly harder,” he said. “It shows how we could manage a border without infrastructure or related checks and control while protecting UK, Northern Ireland, Irish and EU interests.”

The spokesman insisted May and Johnson remained committed to no physical infrastructure at the border, but rather to alternatives as the UK left the customs union.

Earlier, Johnson had sparked anger by comparing the question of solving the Irish border challenge to the London congestion charge system. “There’s no border between Islington, Camden and Westminster, but when I was mayor of London we anaesthetically and invisibly took hundreds of millions of pounds from people travelling between those two boroughs without any need for border checks,” he told BBC Radio 4’s Today programme, calling it a “very relevant comparison”.



Play Video 0:35 'Like the congestion charge': Boris Johnson on Irish border checks post-Brexit – video

Downing Street insisted that Johnson was not offering a “technical solution” to the problem, and added that no conversations were taking place between government officials and Transport for London.

“I thought the foreign secretary was making a comparison to demonstrate our overall approach,” he said, pointing out that there were 110m journeys across the border between Northern Ireland and Ireland annually. People “will continue living their lives as before, travelling freely. Just as Londoners travel across boroughs each day,” May’s official spokesman said.

However, the intervention provoked angry responses. The Fine Gael MEP Mairead McGuinness said the comments were unhelpful, adding that she was no longer shocked by what the foreign secretary had to say.

“On the border question, however, he must realise that two boroughs in London are in the same country. What we are talking about here is the border between the Republic of Ireland and Northern Ireland, which is a part of the UK and therefore in a very different space,” she told BBC Radio 4’s World at One.



Tom Brake, the Lib Dem’s Brexit spokesman and a supporter of the Best for Britain campaign, said Johnson had let the “cat out of the bag”. He said: “Boris Johnson, in spite of claiming today that the border between Northern Ireland and Ireland is no more of a problem than that between Camden and Westminster, knows that the real risk is of a hard border between NI and the Republic of Ireland. He knows this could lead to a resumption of hostilities.”

Arguing that a frictionless border was hard to foresee given the necessity of checking rules of origin, she said: “The solution and the possibilities that he’s proposing by technology fail to understand the history, the geography or the politics.”

Labour politicians also weighed in on Twitter, with the party’s leader in the House of Lords, Lady Smith, saying:

Angela Smith (@LadyBasildon) Did I really hear Boris Johnson, the U.K. Foreign Secretary, compare the Irish border with that between 2 Boroughs in London? No, surely not even Boris could think that?? @BBCr4today

The Open Britain campaign also criticised Johnson. One of its supporters, Chris Leslie MP, said the comparison was “patently ridiculous” and showed “staggering insensitivity and stupefying ignorance of a conflict in which over 3,000 people died between 1969 and the signing of the Good Friday agreement”.

The comments were even referred to in Brussels, where lead negotiator Michel Barnier was holding a press conference before the publication on Wednesday of the document outlining the divorce agreement. Asked about the comparison, he said: “Don’t count on me today to make comments on comments or indulge in polemics. I am focused and I will continue to be focused with all of my time and energy to organise the orderly withdrawal of the UK in line with its wishes and in line with the general interest.”

The official said his task was to achieve that, adding: “What counts here is what the British prime minister says.”

The commission’s text could also cause tension if the EU demands an ongoing role for the European court of justice after Brexit, something that May has been clear is a red line for the government.

She spoke to the taoiseach, Leo Varadkar, by phone on Monday evening to discuss the document that will be published by the commission. “The taoiseach also repeated the necessity from the EU side to have the detail of the backstop option of full regulatory alignment spelled out in the draft legal text of the withdrawal agreement,” Varadkar’s office said. “This option would only come into effect if agreement on one of the other options is not reached.”

The tánaiste, Ireland’s deputy head of government, Simon Coveney, also held talks with Barnier on Monday. Coveney said commitments made in December between the EU and the UK needed to be clearly reflected in new legal text. “EU solidarity remains strong with Ireland’s concerns,” he said after his discussions.

