Sinn Fein has branded as “absolutely bizarre” Arlene Foster’s description of her Brexit red line as blood red, claiming the DUP leader has “lost the run of herself”.

Sinn Fein vice president Michelle O’Neill accused Mrs Foster of being “out of touch” after the former Stormont first minister made clear she would not support any increase in regulatory checks across the Irish Sea as a means to break the deadlock over the Irish border.

Stressing the party’s unwillingness to give ground on the issue, the DUP leader said: “The red line is blood red, it is very red.”

Mrs Foster has insisted that Prime Minister Theresa May needs to show her any new proposals on the Irish border before presenting them to the EU, but she declined to state whether her party would vote against the Government if she considered any proposals unacceptable.

She told BBC Radio Four: “I think we are selling the Prime Minister short, she understands where we are at in all of this and therefore I need to give her that space to share that information with me.”

Her comments came amid reports – denied by senior Conservatives – that the Government was considering allowing more regulatory differences between Northern Ireland and the rest of the UK to ensure a free-flowing Irish border is maintained on the island.

The DUP has made clear it will not countenance any move that would create divisions between Northern Ireland and the rest of the UK’s internal marketplace.

Mrs O’Neill said Mrs Foster’s remarks at the Conservative Party conference in Birmingham showed the DUP was not speaking for the majority view in Northern Ireland, a region that voted Remain.

“I think it demonstrates once again that he DUP have lost the run of themselves,” she said.

“I think the comments themselves are bizarre. They are bizarre in the context that people are worried about their future, their future prosperity, their jobs, the economy, students are worried about how they are going to study across Europe, our rights in terms of the future and what that means for all of us.

“So I think the comments are absolutely bizarre in the context of the serious consequences which there are in regard to Brexit.

“When I look at the last few days and the behaviour of the DUP in England, particular in relation to the Tory party conference, they purport to speak for the people of the North, they do not speak for the people of the North.”

Mrs O’Neill suggested Mrs Foster was attempting to take the focus off a public inquiry into a botched green energy scheme in Northern Ireland, which has seen the actions of senior DUP figures come under intense scrutiny.

“I think the DUP would rather have us talking about blood red lines and everything else to avoid us talking about the calamity that is RHI (Renewable Heat Incentive) and the calamity that is Brexit,” she said.

Sinn Fein’s Stormont leader also reiterated her view that the DUP’s confidence and supply deal with the Conservative Party was standing in the way of restoring powersharing in the region, 21 months after the devolved executive collapsed.

“The biggest fault line in getting an executive up and running is the fact there is a supply and confidence deal between the DUP and the Tories,” she said.

“And I think the DUP are demonstrating it day on day that they are more interested in propping up the Brexiteers than they are in the economic interests, the cultural interests, and the rights of citizens here in the North – that has been demonstrated time and time again.”