THERESA May’s plan for the UK to have no solid border with the Irish Republic post Brexit still threatens to severely disrupt trade, critics claimed today, as Dublin insisted the Northern Ireland peace process should not become a “bargaining chip” in the negotiations with Brussels.

The warnings came as Whitehall this afternoon publishes its “position paper” on how trade across the UK’s only land border with the European Union should continue once the country leaves the Brussels bloc.

Since the Good Friday Agreement ended the Troubles almost 20 years ago, there has been seamless travel between the two states but fears have been raised over a return to border checks following Britain's withdrawal in 2019.

However, a UK Government source declared: “Top of our list is to agree upfront no physical border infrastructure, that would mean a return to the border posts of the past and is completely unacceptable to the UK."

The Prime Minister and her colleagues are considering two options with regard to future customs arrangements: one would align the UK’s system to the EU’s, meaning there would be no need for border checks; the other would use technology to create a “highly streamlined” system to avoid long queues at ports and airports.

However last month, Simon Coveney, the Irish foreign affairs minister, said: "What we do not want to pretend is that we can solve the problems of the border on the island of Ireland through technical solutions like cameras and pre-registration and so on. That is not going to work."

Responding to the UK Government’s Brexit paper, Dublin said: "The emphasis on the priority areas identified by the Government, including the Common Travel Area, the Good Friday Agreement, north/south co-operation and avoiding a hard border, is welcome," but added: "Protecting the peace process is crucial and it must not become a bargaining chip in the negotiations."

The Irish Government said the Brexit paper was "timely and helpful" as it offered more clarity. It said it would now analyse the details and discuss them with the European Commission and Michel Barnier, the Brussels chief negotiator.

In its paper, the UK Government explains how the highly-streamlined customs option might include:

*a continued waiver on submitting entry and exit declarations;

*continued membership of the Common Transit Convention to help companies move goods;

*new “trusted trader” arrangements for larger businesses and

*cross-border trade exemptions, meaning no new customs processes at all for smaller traders with more than 80 per cent of cross-border trade currently undertaken by small and medium-sized firms.

But Tom Brake, the Lib Dems’ Brexit spokesman, denouncing Whitehall’s approach as “shambolic,” said: “It's clear the Government can't deliver on the Leave campaign's promise that the border between Ireland and Northern Ireland border will stay as open as it is now. Even if they only lead to checks on larger traders, these plans could still severely disrupt trade and have a destabilising impact on the region as a whole.

"The only sure way to deliver a truly seamless border is to keep the UK in the customs union and the single market," he added.

Today’s position paper also reaffirms the UK Government's commitment to maintain the almost century-old Common Travel Area, which allows for free movement of UK and Irish citizens around the island, and to uphold the 1998 Good Friday Agreement in "all its parts"; sections of the historic peace accord are underpinned by EU human rights legislation.

Meanwhile, Nicola Sturgeon yesterday denounced the Prime Minister’s plan for a temporary arrangement with the customs union post Brexit as “nonsensical and ridiculous”.

"I wish we weren't leaving the EU,” declared the First Minister. “But if the UK is leaving the EU, then the common sense thing to do is to stay in the single market and to stay in the customs union. Because that will mean we can continue to export goods and services and continue to travel freely like we can today," she added.