SPIRALLING Brexit tensions last night took the Tories’ alliance with the DUP to breaking point as it threatened to torpedo the Budget this month.

The Ulster Unionists threatened the explosive move after being left livid by the latest turn in Brussels negotiations.

5 Arlene Foster threw criticism at the PM from Brussels regarding her plans for Northern Ireland Credit: EPA

With just six days to go until an EU summit to finalise a deal, they fear Theresa May is on the verge of betraying them by enforcing new checks on trade between Northern Ireland and the rest of the UK.

Any government’s failure to pass its annual financial blueprint in the Commons has traditionally been seen as a confidence vote in it.

But as a war of words escalated, Downing Street swiftly hit back to insist the PM would not be forced to quit if the DUP carried out a threat under recent rule changes in the Fixed Terms Parliament Act.

No10 sources also insisted the move would be a clear breach of the Tory-DUP confidence and supply agreement – meaning Ulster would also have to pay back its £1bn bonus from the government.

5 Theresa May surprised her backbench Brexiteers by making her first open appeal to Labour MPs to vote through any Brexit deal she can forge Credit: PA:Press Association

And in an alarming show of force last night, the DUP’s 10 MPs abstained in a routine vote on the government’s Agriculture Bill.

DUP Leader Arlene Foster issued another blunt warning to Mrs May from Brussels yesterday after a second day of talks with EU negotiators.

Ms Foster said: “We’ve been telling people about our red line, we’ve been talking them through it.

“The PM has made a lot of her Unionist credentials over the years since she moved into Downing Street.

5 Michel Barnier has said there should be checks made on goods travelling between the UK and the EU Credit: EPA

“So what’s important is for us to say to her very clearly that any impediment on the two way access in the UK single market would not be good for the union and would not be good for the economy of Northern Ireland.”

As tensions also continued to arise ahead of next week’s EU showdown on the Tory benches, Mrs May also stunned her backbench Brexiteers by making her first open appeal to Labour MPs to vote through any Brexit deal she can forge.

The PM’s plea is a bid to bypass as many as 40 Tory hardliners who have vowed to vote down any deal based around her softer Brexit blueprint.

She told the Commons: “When we come back with a deal, I would hope everybody across this whole house would put the national interest first”.

5 Boris Johnson has warned that the 'backstop' proposals for Northern Ireland would make the UK a 'permanent EU colony' Credit: EPA

Senior Cabinet ministers have been summoned to No10 at 5pm this afternoon for an update from Mrs May on the tense negotiations. But No10 aides played down hopes of any break through, with one telling The Sun: “We’re a way off yet”.

Former foreign secretary Boris Johnson also issued a fresh attack on the PM to warn that the Government’s “backstop” proposals for Northern Ireland would make the UK “a permanent EU colony”.

Labour MPs also dismissed claims that 40 of them will defy their own party whip top vote for the PM’s deal, saying Mrs May would struggler to even persuade over 20 of them.

Mr Corbyn’s spokesman said: “It’s quite clear that the Prime minister is in a very difficult position because she spent most of the last two years negotiating with her own party and not with the European Union and the prospects of a significant rebellion among her own MPs is pretty clear. So it’s not surprising that she’s trying to find support elsewhere and we’ve made very clear what kind of package we would support and what we won’t.”

5 A spokesman for Jeremy Corbyn has said the PM must be in a difficult position as she has spent more time negotiating with her party rather than the EU Credit: PA:Press Association

The EU’s chief negotiator Michel Barnier last night said a Brexit deal is “within reach”, raising hopes of a breakthrough at next Wednesday’s crucial summit and boosting the pound.

Amid expectations of a compromise on the Irish border, he hit back at Arlene Foster’s claim the EU’s backstop would devastate Northern Ireland’s economy.

But he warned some checks between Northern Ireland and mainland Britain will increase tenfold if the UK doesn’t stay in the customs union.

Speaking to business leaders in Brussels the Frenchman said there “must be checks on goods travelling between the EU and UK that don’t exist today”.

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He said all live animals and animal derived food will have to be checked compared to just 10% now, which was “a significant change in terms of scale”.

Under his backstop plan other goods would be subject to “scanning barcodes on ferries or in transit ports” helped by Max Fac style trusted trader schemes.

Mr Barnier said: “There must be checks on goods travelling between the EU and the UK – checks that do not exist today.

“We’re still open to the idea of a customs union with the UK which would eliminate an important part of customs checks.”

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