THE Irish Government has warned Theresa May against using the threat of violence in Northern Ireland as a bargaining chip in Brexit negotiations.

Dublin’s message to the Prime Minister came ahead of the UK government publishing their “imaginative” negotiating proposal on the Irish border, which is due later today.

The Department for Exiting the EU’s positioning paper says London wants to avoid physical checkpoints on the Irish border after Brexit, and believes there should be no “customs implications” as that would not be “constitutionally or economically viable”.

The paper also commits the government to maintaining the almost century-old Common Travel Area (CTA), which allows for free movement of UK and Irish citizens.

It will also include a pledge to uphold the 1998 Good Friday Agreement in “all its parts” – sections of the historic peace accord are underpinned by EU human rights legislation.

A UK Government source said: “Both sides needs to show flexibility and imagination when it comes to the border issue in Northern Ireland and that is exactly what our latest position paper will do.

“As [EU chief negotiator] Michel Barnier himself has said, the solution cannot be based on a precedent so we’re looking forward to seeing the EU’s position paper on Ireland.

“But it’s right that as we shape the unprecedented model, we have some very clear principles. 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.”

Dublin said avoiding a return to the violence of the past should trump everything else.

“The emphasis on the priority areas identified by the Government, including the Common Travel Area, the Good Friday Agreement, north-south cooperation and avoiding a hard border, is welcome,” an Irish Government spokesman said.

“Protecting the peace process is crucial and it must not become a bargaining chip in the negotiations.”

May’s Irish paper comes 24 hours after her government published another positioning paper, proposing a temporary customs union with the EU after Brexit.

Brexit Secretary David Davis said the interim arrangement would avoid “unnecessary disruption” for UK businesses, the so-called “cliff edge”.

It would mean the UK both effectively remaining in the customs union, while also being able to try to negotiate trade deals with other non-EU countries. Under the EU’s rules, you can either do one or the other.

Nicola Sturgeon called Davis’s position “daft”, and tweeted: “Seems UK gov is back to its daft ‘have cake and eat it’ approach to Brexit. They should commit to staying in single market and CU, period.”

Sturgeon later said: “You’ve got the UK Government appearing to say that they don’t want to stay in ‘the’ customs union, but they want to stay in ‘a’ customs union, which would be pretty much identical to the European customs union that we’re in already. It’s nonsensical and ridiculous.

“I think it increasingly makes the UK Government look like a bit of a laughing stock.

“I wish we weren’t leaving the EU, 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.”

The Brexit Secretary’s proposals were also dismissed by Barnier, and Davis had earlier conceded as much.

Asked whether the UK could enact new free trade deals during the temporary period, Davis said “no”, but insisted the leg work could still be done.

“But we should be able to have an arrangement by which we can do the negotiation, sign it off, but not enter [it] into effect,” he added.