Rishi Sunak was warned by the DUP leader that the “wrong” Brexit deal would cement division in Northern Ireland for generations.
Sir Jeffrey Donaldson made the intervention after addressing the European Research Group, made up of hardline Tory Brexiteers, at a gathering behind closed doors in Parliament.
Mr Sunak is trying to secure the backing of both groups behind his proposals for changing post-Brexit trading terms in Northern Ireland, with the details still under discussion with Brussels.
Sir Jeffrey said: “The objective in London and Brussels should be to get this right rather than rushed. The wrong deal will not restore power-sharing, but will cement division for future generations.”
The DUP leader did “commend” the work Mr Sunak had done so far, noting progress had been made, but added: “There’s still some way to go.”
While the comments do not rule out future support of the DUP, the argument that Downing Street should not “rush” to secure an agreement will do little to suggest full backing of an agreement is close.
In the past 48 hours, the Prime Minister has been holding face-to-face with some of the Conservative Party’s most ardent Tory Brexiteers, known as the Spartans, to win them over.
Multiple Tory MPs who have held talks with Mr Sunak told The Telegraph that they stressed the importance of solving the “democratic deficit” in Northern Ireland.
It is a further indication that both the DUP and Tory Brexiteers are closely watching what new role is proposed for the European Court of Justice (ECJ) in the province.
The ECJ is expected by figures involved in UK-EU negotiations to continue to be the ultimate arbiter of issues of EU law in Northern Ireland in any new deal, with Number 10 saying an agreement has not yet been secured.
However, some close to the process believe that London and Brussels will issue a joint statement which will stress that using the ECJ will only be a matter of last resort.
Mr Sunak is hoping to sign and seal an agreement with Brussels that convinces the DUP to return to power-sharing in Stormont and avoids a large Tory backbench rebellion.
Achieving all three would be a political triumph, given that both Boris Johnson and Liz Truss, in her brief premiership, failed to square Brussels behind Protocol changes.
But the challenge of getting the backing of the DUP, which has set seven tests for any new deal, and the ERG has been underscored by non-committal public comments from figures in both groups in recent days.
Tuesday had been pencilled for the deal’s reveal in the House of Commons, according to Whitehall insiders, but the timings have slipped as discussions continue.
After his meeting with Eurosceptics, Sir Jeffrey also said: “Over 18 months ago we outlined the parameters for the way forward. We set our tests and those continue to be our yardstick for measuring any deal between the EU and UK.
“The checks on the Irish Sea border are the symptom of the underlying problem, namely, that Northern Ireland is subject to a different set of laws imposed upon us by a foreign entity without any say or vote by any elected representative of the people of Northern Ireland.
“There will be no restoration of the NI Executive until the Protocol is replaced with arrangements that are good for Northern Ireland and its place in the United Kingdom.”
Sir Jeffrey also said it would be “not acceptable” if the ECJ retained oversight of goods produced in Northern Ireland travelling to the mainland UK, one of the reported sticking points.
EU control ‘is colonial status’
An opinion poll of Red Wall seats, released on Tuesday, put Labour 28 percentage points ahead of the Tories, the highest lead on the tracker since Mr Sunak took office.
Numerous Tory MPs who saw Mr Sunak for talks told The Telegraph about their discussions and thinking after the conversation.
One Tory MP said: “We really do need to stop Northern Ireland being subject to rule by a foreign government. It’s colonial status. If the EU don’t change their mandate, there can’t be any replacement to the Protocol.
“If that’s the case, we shouldn’t do the deal because it isn’t really a deal. It’s effectively the same arrangements we have at the moment, but with a bit of tweaking.
“The importance of the DUP can’t be overstated – they are terrifically important in this process.”
A second Tory MP raised the democratic deficit: “I think I made them very aware of the fact this was an issue of such importance and they themselves seemed to understand.
“The important question is how strongly are you getting a message across, and I distinctly got the impression my message was received and well understood.
“I’ve asked for the Protocol Bill to be carried forward over and over again. There isn’t a single democratic country in the world which has laws passed over the heads of its citizens.”
Meanwhile, Tory infighting over Brexit erupted in public after Theresa May’s former chief of staff told Eurosceptic MPs to back Rishi Sunak’s Northern Ireland deal.
Lord Barwell said that backbenchers should “get behind” the Prime Minister’s attempts to fix the Protocol, given that they were responsible for it in the first place.
He clashed with Simon Clarke, a former Cabinet minister and leading Brexiteer, who said it was Mrs May’s failure to stand up to Brussels that created the mess.
The public spat, which unfolded on social media, laid bare the huge divisions within the Conservatives over how to end the stalemate in Northern Ireland.
Jacob Rees-Mogg has compared Mr Sunak’s approach to securing a Brexit deal with the EU to that followed by Theresa May when she was prime minister.
Speaking on The Moggcast podcast, published by the ConservativeHome website, the former Brexit opportunities minister said: “I don’t know why so much political capital has been spent on something without getting the DUP and the ERG onside first.
“It is quite surprising because this is very similar to what happened with Theresa May.”