THERESA May’s plans for a soft border between Northern Ireland and the Republic after Brexit have been rejected as unworkable under a hard Brexit.

The SNP MEP Alyn Smith said he saw no way of preventing the emergence of a physical border with customs posts and checks in the event of the UK leaving the single market and customs union.

He spoke out last night after the UK Government published a 28-page position paper setting out proposals for avoiding such measures.

“Having read this paper I don’t see how they are going to deliver what the UK Government allegedly seek to deliver in this paper,” he said.

“If goods remained in the single market the problems don’t arise, but the Brexiteers don’t want to remain in the single market which would mean being subject to the four freedoms of free movement of workers, capital, goods and services.

“But Ireland is going to remain in the single market, so there is going to be a proper border at Gibraltar and in Ireland. The UK Government is still not getting it. The practicalities [of avoiding a hard border while the UK leaves the single market] are insurmountable.”

He added: “I suspect the reaction from Dublin to this paper will be ‘that’s not going to work’... and there is absolutely no doubt the other 27 member states will be backing Irish interests and the British have alienated any potential support which was there.”

The UK Government stresses there should be no physical infrastructure at the border, which has about 200 crossing points and nor does it envisage CCTV cameras or number plate recognition technology at the border, or set back from it.

Ministers want to avoid the need for such physical controls, seeing an open border allowing people to cross freely between both parts of Ireland as essential to preserving the Good Friday peace agreement. Such an arrangement has been in place for almost a century since the Common Travel Area was introduced after Irish independence.

In terms of trade, the paper proposes a series of waivers which would see 80 per cent of businesses on the island entirely exempt from any new tariffs post-Brexit. The exemption would apply to small and medium-sized enterprises involved in localised cross-border trade.

Larger companies engaged in international trade, could adhere to any new customs regime by completing retrospective declarations either online or at their premises, the paper says.

Officials concede the proposals could be open to fraud — with Great Britain or continental European-based companies using Irish business counterparts to avoid tariffs — but they believe those risks can be managed effectively.

Sinn Fein’s Stormont leader, Michelle O’Neill, said the proposals were “big on aspiration but light on clarity” as she reiterated her party’s appeal for Northern Ireland to retain special designated EU status post-Brexit and called on the Irish Government to “defend the rights” of the 56 per cent of Remain voters north of the border. Democratic Unionist leader and former Stormont First Minister Arlene Foster described the paper as a “constructive step”.

The Irish border is a priority for the EU and the UK paper also seeks to persuade the bloc to continue funding for peace initiatives in Northern Ireland post Brexit. Negotiations restart on 28 August.