Theresa May’s minority government pact appeared on shaky ground after several DUP MPs voted in support of a Labour Budget amendment.
The Prime Minister struck a “confidence and supply” arrangement with the 10 DUP MPs, secured with a controversial £1 billion funding deal for Northern Ireland, after she lost her majority following the snap election in June 2017.
But eight MPs opted to support a Labour amendment to the Finance (No. 3) Bill, according to the division list.
Labour’s new clause two aimed to force the Government to review the impact of increases to the personal allowance on child poverty and equality.
This meant the Government only defeated the proposal by 292 votes to 287, majority five.
The DUP had already abstained on the opening two votes at the Bill’s committee stage, and also did not vote during the fourth division of the day.
Tensions between the two parties have increased in recent weeks over Brexit.
Shadow Cabinet Office minister Jon Trickett said in a statement outside the Commons: “We no longer have a functioning government.
“With Brexit only a few months away something has got to give.”
The Government was later forced to make a concession after several Tory MPs, including former minister Jo Johnson, signed a Brexit-linked amendment moved by Labour’s Chuka Umunna.
Mr Umunna’s amendment sought to force the Government to publish economic forecasts to allow the impact of the EU withdrawal agreement, remaining in the EU and leaving with no deal to be compared.
Treasury minister Robert Jenrick confirmed the Government will provide economic modelling of three Brexit scenarios compared to the status quo.
He told MPs: “I’m happy to confirm the baseline for this comparison will be the status quo - that is today’s institutional arrangements with the EU.
He added: “I can confirm this analysis will bring together evidence from across Government, external stakeholders and a range of analytical tools.
“The analysis will consider the long-term costs and benefits of moving to new trading relationships with the EU and with the rest of the world.
“The analysis will consider a modelled no-deal scenario - or World Trade Organisation terms - a modelled analysis of a free trade agreement scenario, and a modelled analysis of the Government’s proposed deal.”
Mr Umunna, in a statement issued outside the chamber by the People’s Vote campaign, said: “The Government was planning to con the British people.
“It is vital at this crucial time for our country that MPs and the public know the full facts about the cost of Brexit and how it compares to the deal we already have inside the EU.”
Shadow economic secretary Jonathan Reynolds welcomed the concession, but told MPs: “I think, reflecting the parliamentary arithmetic, I’m not sure they did it voluntarily until they saw the names on the order paper.”
He added: “Transparency about the consequences of different types of Brexit arrangements has got to be a good thing, and the country and all of us in this House should be as well-informed as possible in that situation so it’s extremely pleasing to see the Government concede on this point.”
Former rail minister Jo Johnson, speaking in support of Mr Umunna’s amendment, said the concession was a case of “better late than never”.
He added: “If we’ve learnt anything from the chaos of the last 30 months, it is that facts are sacred. This is a debate which has been characterised by falsehoods and misinformation from day one.
“It’s extraordinary that we’ve now had to force the Government at this relatively late stage to publish vital information necessary for an informed public debate.”
“Given that the reality of Brexit has proved to be so far from what was once promised during the campaign, the democratic thing to do is not just accept amendment 14 but to publish the like for like economic analysis that shows how costly Brexit will be, the democratic thing to do is also to give the public a final say about whether they really want to proceed on this hopeless basis”, he added.