Significant gaps in Theresa May’s new Brexit customs plan for Northern Ireland would lead to the creation of a hard border with the Republic, the European Commission has said.

A presentation drawn up by the EU’s negotiating team for member states said the UK’s customs paper, which was released on Thursday, “leaves key questions unanswered”.

Officials are particularly worried that the UK plan would not keep Northern Ireland aligned with single market rules, meaning regulatory checks would be needed at the border for goods.

They are also concerned at UK proposals to time-limit the proposal until 2021 at the latest, with the presentation asking: “Is this a backstop?”

The presentation concludes that the UK proposal “does not cover regulatory controls, leading to a hard border”.

Brexit secretary David Davis met with chief negotiator Michel Barnier in Brussels on Monday to discuss progress in the negotiations. The trip is only Mr Davis’s second visit to the de facto EU capital this year, with progress in talks having been slow. The minister declined to speak to the press during the trip.

The “backstop solution” is supposed to prevent a hard border from emerging on the island of Ireland no matter what happens. Both sides say they do not want a hard border because the open frontier is part of the Good Friday Agreement, which brought an end to the Troubles.

Mr Barnier last week said he was still studying the UK’s proposal and had not rejected it out of hand. When asked why he was doing so if it has such problems, he said: “Because I look at all British proposals in an objective manner.”

The UK paper is the product of months of cabinet wrangling over how to temporarily solve the Irish border issue if it cannot be solved by a wider trade deal.

Separately, the cabinet has still not decided on a single solution for the wider customs agreement between the UK and EU – with two options on the table. Both ideas, “max fac” and “customs partnership” have been rejected out of hand by Brussels.

A spokesperson for the European Commission said: “We can confirm that the European Commission chief negotiator Michel Barnier and the secretary of state for exiting the European Union David Davis met this morning here in Brussels where they discussed the latest state of play of the Article 50 negotiations. They touched on issues related to the withdrawal agreement, including the backstop for Ireland-Northern Ireland and the framework for the future relationship.”

British officials confirmed a similar line; neither side would give more details.

Brexit threatens life on the Irish border: in pictures Show all 15 1 /15 Brexit threatens life on the Irish border: in pictures Brexit threatens life on the Irish border: in pictures An abandoned shop is seen in Mullan, Co Monaghan. The building was home to four families who left during the Troubles. The town was largely abandoned after the hard border was put in place during the conflict. Mullan has seen some regeneration in recent years, but faces an uncertain future with Brexit on the horizon Reuters Brexit threatens life on the Irish border: in pictures A defaced ‘Welcome to Northern Ireland’ sign stands on the border in Middletown, Co Armagh Reuters Brexit threatens life on the Irish border: in pictures Mervyn Johnson owns a garage in the border town of Pettigo, which straddles the counties of Donegal and Fermanagh. ‘I’ve been here since 1956, it was a bit of a problem for a few years. My premises has been blown up about six or seven times, we just kept building and starting again,’ Johnson said laughing. ‘We just got used to it [the hard border] really but now that it’s gone, we wouldn't like it back again’ Reuters Brexit threatens life on the Irish border: in pictures Farmer Gordon Crockett’s Coshquin farm straddles both Derry/Londonderry in the North and Donegal in the Republic. ‘At the minute there is no real problem, you can cross the border as free as you want. We could cross it six or eight times a day,’ said Crockett. ‘If there was any sort of obstruction it would slow down our work every day’ Reuters Brexit threatens life on the Irish border: in pictures John Murphy flies the European flag outside his home near the border village of Forkhill, Co Armagh Reuters Brexit threatens life on the Irish border: in pictures Potter Brenda McGinn stands outside her Mullan, Co Monaghan, studio – the former Jas Boylan shoe factory which was the main employer in the area until it shut down due to the Troubles. ‘When I came back, this would have been somewhere you would have driven through and have been quite sad. It was a decrepit looking village,’ said McGinn, whose Busy Bee Ceramics is one of a handful of enterprises restoring life to the community. ‘Now this is a revitalised, old hidden village’ Reuters Brexit threatens life on the Irish border: in pictures Union Flag colours painted on kerbstones and bus-stops along the border village of Newbuildings, Co Derry/Londonderry Reuters Brexit threatens life on the Irish border: in pictures Grass reflected in Lattone Lough, which is split by the border between Cavan and Fermanagh, seen from near Ballinacor, Northern Ireland Reuters Brexit threatens life on the Irish border: in pictures Donegalman David McClintock sits in the Border Cafe in the village of Muff, which straddles Donegal and Derry/Londonderry Reuters Brexit threatens life on the Irish border: in pictures An old Irish phone box stands alongside a bus stop in the border town of Glaslough, Co Monaghan Reuters Brexit threatens life on the Irish border: in pictures Billboards are viewed from inside a disused customs hut in Carrickcarnon, Co Down, on the border with Co Louth in the Republic Reuters Brexit threatens life on the Irish border: in pictures Seamus McQuaid takes packages that locals on the Irish side of the border have delivered to his business, McQuaid Auto-Parts, to save money on postal fees, near the Co Fermanagh village of Newtownbutler. ‘I live in the south but the business is in the North,’ said McQaid. "I wholesale into the Republic of Ireland so if there’s duty, I’ll have to set up a company 200 yards up the road to sell to my customers. I’ll have to bring the same product in through Dublin instead of Belfast’ Reuters Brexit threatens life on the Irish border: in pictures A disused Great Northern Railway line and station that was for customs and excise on the border town of Glenfarne, Co Leitrim Reuters Brexit threatens life on the Irish border: in pictures Alice Mullen, from Monaghan in the Republic of Ireland, does her shopping at a former customs post on the border in Middletown, Co Armagh. ‘I’d be very worried if it was a hard border, I remember when people were divided. I would be very afraid of the threat to the peace process, it was a dreadful time to live through. Even to go to mass on a Sunday, you’d have to go through checkpoints. It is terribly stressful,’ said Mullen. ‘All those barricades and boundaries were pulled down. I see it as a huge big exercise of trust and I do believe everyone breathed a sigh of relief’ Reuters Brexit threatens life on the Irish border: in pictures A bus stop and red post box stand in the border town of Jonesborough, Co Armagh Reuters

Officials on both sides are getting ready for a European Council summit in March where member states will take stock over the state of negotiations so far.

A UK Government spokesperson said: “The Prime Minster has been clear that we will never accept a customs border between Northern Ireland and the rest of the United Kingdom.

"We are also committed to maintaining the integrity of our own internal market. That position will not change. The Commission’s proposals did not achieve this, which is why we have put forward our own backstop solutions for customs.