The Government has responded cautiously to the prospect of a new customs partnership arrangement proposed by the British prime minister as a way of avoiding a hard border.

Theresa May is understood to favour a scheme which would see the UK act as an external frontier for the European Union and collect tariffs and carry out other checks on imports.

However, the initiative has been described as “magical thinking” by officials in Brussels and could take many years to introduce, potentially derailing the Brexit timetable.

A Government spokesman said it was the position of Taoiseach Leo Varadkar that the solution to the Border must be one that satisfies the UK and the EU.

While Ms May’s proposal had not been ruled out, the spokesman indicated such an arrangement would “take a long time to negotiate and prepare for implementation”.

“Any solution will have to deliver on the commitment to avoid a hard border and protect North/South co-operation, while simultaneously protecting the EU’s single market and customs union. It will also need to be spelled out in legal detail.

“Pending agreement on the detail of any such solution, the backstop option of full regulatory alignment will have to be included in the Withdrawal Agreement.”

The scheme is to be raised with EU officials this month and appears to be the work of a new British ministerial group on Northern Ireland.

Chancellor Philip Hammond, Cabinet Office minister David Lidington and Northern Ireland secretary Karen Bradley have been tasked with overseeing planning for the Irish Border.

A spokesman for Tánaiste Simon Coveney said he would not be engaging in a running commentary on the Brexit discussions.

The place to discuss proposals for the future relationship is at “the negotiating table” and with the taskforce headed by EU chief negotiator Michel Barnier, he added.

Britain is promoting the “customs partnership” plan as the best way to avoid disruption at the ports, and the Border.

This was proposed first by the British Government a number of months ago but was resisted by European officials.

Forum

Meanwhile, Sinn Féin leader Mary Lou McDonald has called on the Government to stand up to the British Conservative party on the convening of the British-Irish intergovernmental conference in Northern Ireland.

Mr Varadkar and Mr Coveney have expressed their support for the establishment of such a forum, but London has so far resisted the requests.

Ms McDonald said the delay in doing so is proving to be “very damaging” and “not helpful”.

She added: “It is unwise for Dublin to allow the Tories to stall things to this extent and I really hope that when we return from the Easter recess that we see a new determination within Government to make that intergovernmental conference happen and to be quite insistent that we have a plan.”

Under an intergovernmental conference, the Government can have an input into non-devolved matters relating to the North.

Mr Coveney has raised the issue of the conference with Ms Bradley, but the British government has so far been non-committal.

A spokesman for the Tánaiste said the matter would be discussed with the Northern Secretary at a meeting after the Easter recess.