Boris Johnson joined with senior Democratic Unionists to demand the scrapping of the Irish border backstop at a party conference dominated by the draft Brexit deal.
The former foreign secretary, who was guest speaker at the annual DUP gathering in Belfast, also stressed the need for the Tories to protect their faltering confidence and supply agreement with the Northern Ireland party amid ongoing Brexit uncertainty.
Addressing the DUP faithful, Mr Johnson echoed calls from party leader Arlene Foster and deputy leader Nigel Dodds for the Prime Minister to bin the proposals that could see the region operate under different regulatory rules to the rest of the UK post-Brexit.
“Unless we junk this backstop, we will find that Brussels has got us exactly where they want us - a satellite state,” said the Tory MP.
He warned the draft Brexit deal is in danger of turning Northern Ireland into an “economic semi-colony” of the EU.
The backstop proposal in the Withdrawal Agreement would see Northern Ireland adopt a different regulatory regime to Great Britain in the event a wider UK/EU trade deal fails to materialise in talks on the future relationship.
It has been included to ensure a free flowing Irish border regardless of what sort of Brexit unfolds.
The DUP is vociferously opposed to it, claiming it would divide up the UK.
In her leader’s speech, Ms Foster told DUP delegates that while she believes Theresa May is “genuine” in her desire to protect the Union, the draft deal fails to do that.
“The Prime Minister has not been able to guarantee an outcome that eliminates the risk of the introduction of the so-called backstop arrangements,” she said.
The DUP conference appeared more understated than in previous years. The was a markedly different tone, with no party singsongs or mass distributions of Union flags for delegates to wave - usually familiar sights at the annual gatherings.
Ms Foster had also used her speech to apologise for her party’s role in Stormont’s botched green energy scheme - the Renewable Heat Incentive (RHI) - after a catalogue of failings by senior DUP figures were laid bare at a public inquiry.
“Some of our past decisions and actions have left a lot to be desired and I know that they have personally hurt and offended many of our members, voters and the public,” she said.
“I make no excuses. Today, as leader of the party, I apologise.
“As a party we are deeply, deeply sorry for the mistakes we made and for the things we got wrong during that period.”
Turning to Brexit, Ms Foster acknowledged the frustration of many in Northern Ireland’s business community with the pace of negotiations.
Her DUP has prided itself on its relationship with business leaders, but those links have been strained by the support many of them have voiced for the draft UK-EU deal in recent days.
Ms Foster said the constitutional implications of the deal could not be ignored.
“We are not campaigning for a no-deal exit nor do we want barriers to trade between Northern Ireland and our neighbours in the Republic,” she said.
“The choice is not between this deal and no deal, despite what the Government spin machine may say.
“The reality is that if we are to secure a better outcome than is currently on offer, then the only option is to look beyond this current draft Withdrawal Agreement and work in the time ahead for an improved outcome.
“The days and weeks ahead will be challenging. We will continue to work in Parliament to achieve the best possible deal for Northern Ireland and the UK as a whole, guided by our principles and objectives.”
In media interviews ahead of the conference, Ms Foster, a strong critic of Jeremy Corbyn, claimed Ms May’s deal would be a worse outcome for the UK than a Labour government led by him.
But she also warned the DUP would revisit its confidence and supply deal to support the Conservatives at Westminster if the Brexit agreement is voted through Parliament.
After a week that saw the DUP refuse to support the Government in Commons votes to signal their anger at the draft withdrawal text, Mr Johnson stressed the need to maintain the “crucial” confidence and supply deal going forward, warning of ruinous consequences for the UK if Mr Corbyn came to power.
“And so to our allies in the DUP, I hope that you agree that it is absolutely vital that we keep this partnership going and that we are not so complacent as to abandon the government of this country to a man whose avowed policy is to break up this country,” he said.
“And we should work together to ensure that the whole UK - Northern Ireland included - can seize the opportunities of Brexit.”
In his conference speech, Mr Dodds insisted it is not too late to bin the Brexit deal.
He urged Mrs May to change course, warning the proposed Withdrawal Agreement would see the UK assume a “pitiful and pathetic place”.
The party’s Westminster leader insisted the union of Great Britain and Northern Ireland is “non-negotiable”.
He said: “It is still not too late for the Prime Minister to change course.
“Don’t believe the propaganda that it’s too late - it isn’t.
“The DUP wants a deal with the European Union, we understand that businesses, families and communities want certainty.
“But it is not this deal. It is not a deal at any price. The Prime Minister used to say that. We still say that.
“So Prime Minister, the message from this conference, from every section of this party, is - bin the backstop.”
The position of Gibraltar had been one of the issues facing EU states attempting to agree a common position on UK withdrawal, as Spain pressed for guarantees over its say on the future of the British territory.
On Saturday morning, a government minister from Gibraltar told the DUP conference it “will not fold” in the face of Spain’s Brexit demands.
Samantha Sacramento was given a rousing reception by DUP members as she insisted Gibraltar will not be “bullied” by any bid from Madrid to undermine its sovereignty.
Housing and equality minister Ms Sacramento was standing in for Gibraltar’s chief minister, Fabian Picardo.
He had been due to address the party conference but the renewed focus on the British territory in the Brexit talks forced him to pull out to concentrate on the negotiations.