DUP leader Arlene Foster has warned its “red line” that there could be no Brexit deal that would divide Northern Ireland from the rest of the United Kingdom was “blood red”.

With reports that the UK is preparing to move its position on the legal text of the border backstop – the guarantee of no hard border in Ireland – the DUP has insisted it would vote against any proposal that would result in any new barriers between the North and the rest of the UK.

“There cannot be a border down the Irish Sea, a differential between Northern Ireland and the rest of the UK,” Ms Foster told the BBC on Tuesday. The interview was aired on Wednesday.

“The red line is blood red,” she said.

“All along we have said: ‘No new regulatory alignment.”

The DUP’s 10 MPs prop up British prime minister Theresa May’s minority Conservative government.

When asked if she was prepared to vote down Ms May on a Brexit deal, Ms Foster said: “We don’t want to be in that position.

“This is too important to be playing around with things because this is the union - this is what brought me into politics.”

Sinn Féin branded Ms Foster’s comments as “absolutely bizarre”, claiming the DUP leader has “lost the run of herself”.

Sinn Féin vice president Michelle O’Neill accused Ms Foster of being “out of touch”.

The Government clashed publicly on Tuesday with the DUP over Brexit and the future of the Belfast Agreement, with Taoiseach Leo Varadkar rejecting suggestions the agreement could be changed to accommodate Brexit.

While Ms Foster had suggested the agreement “wasn’t sacrosanct”, Mr Varadkar told the Dáil it “is not a piece of British legislation”.

“It is an international agreement between the British and Irish governments as well as a multi-party agreement among the various parties,” he said.