Boris Johnson has refused to back Rishi Sunak’s Brexit deal in a major blow to Downing Street’s hopes of avoiding a eurosceptic rebellion.
The former prime minister said the “best way forward” is instead to press ahead with a law that would rip up the existing Irish border agreement with the EU.
In an interview, Mr Johnson insisted that passing the Protocol Bill would “fix all the problems” faced by people and businesses in Northern Ireland.
His remarks will dent Number 10’s hopes of winning round Conservative MPs and the Democratic Unionist Party (DUP), who have expressed concern over the contents of Mr Sunak’s deal.
Downing Street had been braced for Mr Johnson’s opposition, with Mr Sunak’s allies arguing that he is motivated by a wish to return to power.
The former prime minister was asked twice during an interview with Sky News whether he could commit to supporting an agreement with the EU.
“I think that it’s important we wait to see what there may be, but I think the best way forward is the Northern Ireland Bill,” he told the broadcaster.
“It fixes all the problems. It solves the problems that we have in the Irish Sea, it solves the problems of paperwork, VAT and so on.
“It’s an excellent Bill and doesn’t set up any other problems in the economy of the whole island of Ireland, so I’d go with that one.”
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His intervention comes amid fears in Brussels and European capitals that the backlash to the proposed deal in Westminster is “spiralling out of control”.
EU officials and diplomats voiced fears that Mr Sunak will be unable to secure the backing of the DUP or the European Research Group (ERG) of Tory MPs.
“I’m starting to wonder whether a deal is possible at all,” one source told The Telegraph.
An EU diplomat added: “It seems like things are spiralling out of control for No 10, so we might soon find out.
“Sunak’s been waiting for the moment to jump and get this done politically. The question is whether he’s waited too long.”
The UK and EU have been engaged in intensive negotiations in the hope of finalising a deal to end the two-year stand-off over the Protocol. It prevents a hard border with Ireland by moving checks to the Irish Sea, but Unionists argue that it has created barriers between Northern Ireland and Great Britain.
Mr Sunak has opened talks with Unionists and Brexiteers to start selling the reformed deal that he has all but agreed with Brussels.
The Prime Minister has argued that the pact delivers on the demands set out by the DUP and ERG without making the finer details of it public, but they appear unconvinced.
Both the EU and UK had planned to close the deal by the end of the month, which now looks increasingly unlikely.
Once a deal is agreed, it will be finalised at a meeting between Mr Sunak and Ursula von der Leyen, the European Commission’s president, in London.
The apparent breakdown has left some eurocrats pondering whether they could have forced Mr Sunak’s hand by pushing a “quick and dirty” deal through under the radar last month.
“I think there was merit in us coming out swiftly and randomly, but it is too late now,” said a source.
Some negotiators blame the fact that the Prime Minister kept the DUP and ERG in the dark for too long over his planned deal, which retains powers for European judges in Northern Ireland.
Others believe No 10 has failed in its sales pitch by refusing to reveal details that suggest Brussels went further with its concessions than planned to get the deal over the line.
Meanwhile, the prospect of Mr Sunak winning over the DUP appeared to shrink further, as a former leader warned its hardline stance would not be dropped.
Baroness Foster, a former leader of the DUP, warned the Prime Minister that the party has a “mandate” from Northern Irish voters for its tough stance.
She said that Mr Sunak’s decision not to consult Unionists before sewing up the deal was “bizarre” and reminiscent of Theresa May’s approach.
“It is amazing that the tactics that have failed in the past should be used again and that they don’t expect the same outcome,” she told The Telegraph.
“I would’ve thought working with the leadership of the party was the way to try and find a solution. This whole thing about them not wanting a deal is wrong.”
She warned the Prime Minister that signing off on any agreement that does not have DUP support “achieves nothing and actually makes things worse”.
“If he’s determined to go ahead, it will not bring back devolution in Northern Ireland and he will have to bear the responsibility for that along with the EU,” she said.
Tory MPs have sympathy with Mr Sunak, who they said is “doing his best” – but said the politics of it had been handled “appallingly” by Downing Street.
“The truth is they’ve had a bit of a shock because they thought they had a cunning plan,” one eurosceptic backbencher said on the delay to announcing a deal.
“They thought it was going to go swimmingly and now they’ve realised that certain people have got certain concerns and they’ve got to address that.”
Bertie Ahern, a former Irish prime minister, suggested that the EU would be willing to hold on and sign the deal with Sir Keir Starmer if it is blocked by Tory MPs.
“If it’s not sorted in the next few weeks, we will have to wait until the next British government, which looks like it will be a Labour government,” he said.
In a speech on Thursday, Sir Keir pledged to forge closer ties with Europe which would include “improving” the current trade deal.
“We have to have a closer trading relationship, not just fixing the Protocol in Northern Ireland but more generally,” he said.
Penny Mordaunt, the Commons Leader, said any agreement would “alleviate friction” facing businesses and “address the democratic deficit for the people of Northern Ireland”.
She said the Protocol Bill, which would give ministers the power to rip up border checks in the absence of a deal, “is quite helpful in focusing minds to get the right result”.