TENSIONS over Brexit and the Irish border have intensified with Arlene Foster accusing Ireland’s Taoiseach of being “reckless” and warning him not to “play around” with Northern Ireland.

The criticism from the Democratic Unionist leader came as Simon Coveney, Ireland’s Foreign Minister, issued his own warning to Theresa May, saying that simply upping the cost of Britain’s divorce bill would not be enough to open the door to trade talks with Brussels; Dublin wants a guarantee of an open border between the Republic and Northern Ireland.

Last week, Leo Varadkar, the Irish premier, made clear Dublin would block the progress of the Brexit negotiations in December unless the UK gave a formal written guarantee that there would be no hard border with Northern Ireland.

He called for “further concessions” and insisted a Brexit deal was “not even close”.

But Ms Foster told the BBC she was accusing the Irish Government of “being reckless because…there are people that will come out and will say things to try and push agendas forward and we do recognise that we are at a critical phase because we all, well, certainly I, want to see the negotiations move to the second phase so that we can talk about those issues of trade…that will make a difference in relation to the border between Northern Ireland and the Republic of Ireland”.

Asked if she was warning off Mr Varadkar, the DUP leader replied: “I'm saying to him that he should know better than anybody that you don't play around with Northern Ireland to effect change in other places…”

She added: “I recognise the UK leaving the European Union is a big shock for the Republic of Ireland and they're trying to process all of that. But they certainly shouldn't be using Northern Ireland to get the maximum deal for their citizens. What they should be doing is working with us, working with the rest of the United Kingdom because of course, the biggest market for the Republic of Ireland is GB.”

However, Mr Coveney echoed the Taoiseach, suggesting Ireland had a veto on a Brexit deal and would be prepared to use it.

He told the London Evening Standard: “Anybody who thinks just because the financial settlement issue gets resolved…that somehow Ireland will have a hand put on the shoulder and be told: ‘Look, it’s time to move on.’ Well, we’re not going to move on…This is a much bigger issue than trade. This is about division on the island of Ireland.”

At Westminster, Boris Johnson said a hard Irish border would be "madness" as Labour urged him to set a red line or prepare to resign over the issue.

During Foreign Office Questions Labour’s Emily Thornberry reminded the Foreign Secretary of his February 2016 pledge that Brexit would leave Irish border arrangements "absolutely unchanged" and asked him to give the same promise.

Mr Johnson did so, declaring: “There can be no hard border; that would be unthinkable. It would be economic and political madness.”

Earlier, David Davis, the Brexit Secretary, speaking at a Deal or No Deal conference in London, said: “Whatever happens, we are leaving the European Union and delivering on the instructions of the British people. I don't think it would be in the interests of either side for there to be no deal.”

In other developments –

*Downing Street insisted the jurisdiction of the European Court of Justice over EU nationals in the UK would end after the two-year transition period following Brexit; this came after Brandon Lewis, the immigration minister, suggested the issue of a continuing role for the ECJ after the transition period was "part of the negotiations".

*Stephen Martin, Director General of the Institute of Directors, warned the Prime Minister she would need to secure a clear Brexit transition agreement by March if she wanted to avoid a “snowballing” number of companies activating contingency plans and even moving operations out of the UK.

*Christian Schmidt, the German food minister, warned Britain to resist pressure from Tory Brexiteers like Jacob Rees-Mogg to drive a harder bargain on the financial settlement following the collapse of Angela Merkel’s coalition talks. “My suggestion is just to think what kind of disaster this would be for the United Kingdom's economy,” he said.