Theresa May has been dealt a fresh blow after MPs forced the government to agree to publish analysis comparing the economic impact of her Brexit deal with staying in the EU.

A cross-party amendment outlining the demand was backed by more than 70 MPs from six political parties, including enough Conservative rebels to deprive the government of its majority.

Facing the prospect of a humiliating Commons defeat, ministers bowed to pressure and agreed to accept the motion.

It means that, before MPs vote on Ms May’s Brexit deal, the government will have to publish analysis comparing the impact of the proposed agreement with the consequences of the alternative scenarios of a no-deal Brexit and remaining in the EU.

The information will be made available at least a week before MPs hold a ”meaningful vote“ on whether or not to accept Ms May’s Brexit deal.

The amendment to the Finance Bill was tabled by Labour MP Chuka Umunna and Conservative former minister Anna Soubry, who have been at the forefront of attempts to force a fresh referendum on Brexit.

Tory backers of the motion included Jo Johnson, who resigned as a transport minister earlier this month in order to criticise Ms May’s Brexit plan.

The government has previously promised to publish Treasury analysis of the impact of the prime minister’s deal compared to a no-deal outcome, but it was not expected to release a comparison with the outcome of Britain remaining in the EU.

Less than an hour before a scheduled vote on the amendment, Treasury minister Robert Jenrick confirmed the government would publish the full set of comparisons.

He told the Commons: “The government has already confirmed that before we bring forward the vote on the final deal, we will ensure that parliament is presented with the appropriate analysis in good time to make an informed decision.

“I can confirm that this analysis will bring together evidence from across government, insight from external stakeholders, a range of data and analytical tools. The analysis will consider the long-term costs and benefits of moving to new trading relationships with the EU and the rest of the world.”

Cabinet ministers resign over Brexit deal Show all 13 1 /13 Cabinet ministers resign over Brexit deal Cabinet ministers resign over Brexit deal Esther McVey Britain's Work and Pensions Secretary Esther McVey arrives to attend the weekly meeting of the cabinet at 10 Downing Street in London. - Britain's Work and Pensions Secretary Esther McVey resigned from the cabinet over draft Brexit deal AFP/Getty Cabinet ministers resign over Brexit deal Handout image taken from the Twitter feed of @EstherMcVey1 of the resignation letter addressed to Prime Minister Theresa May from Works and Pensions Secretary Esther McVey. PRESS ASSOCIATION Photo. Issue date: Thursday November 15, 2018. Ms McVey has resigned, saying the Brexit deal âdoes not honour the result of the referendumâ. See PA story POLITICS Brexit. Photo credit should read: @DominicRaab/PA Wire NOTE TO EDITORS: This handout photo may only be used in for editorial reporting purposes for the contemporaneous illustration of events, things or the people in the image or facts mentioned in the caption. Reuse of the picture may require further permission from the copyright holder. PA Cabinet ministers resign over Brexit deal Dominic Raab British Brexit Secretary Dominic Raab give a press conference at the end of the final round of talks in Brexit negotiations at the European Commission in Brussels, Belgium EPA Cabinet ministers resign over Brexit deal Handout image taken from the Twitter feed of @DominicRaab of the resignation letter addressed to Prime Minister Theresa May from Brexit Secretary Dominic Raab. PRESS ASSOCIATION Photo. Issue date: Thursday November 15, 2018. Mr Raab has resigned, saying he âcannot in good conscience support the terms proposed for our deal with the EUâ. See PA story POLITICS Brexit. Photo credit should read: @DominicRaab/PA Wire NOTE TO EDITORS: This handout photo may only be used in for editorial reporting purposes for the contemporaneous illustration of events, things or the people in the image or facts mentioned in the caption. Reuse of the picture may require further permission from the copyright holder. PA Cabinet ministers resign over Brexit deal Rehman Chrishti Vice Chairman of the Conservative Party Rehman Chrishti tendered his resignation letter this afternoon PA Cabinet ministers resign over Brexit deal Cabinet ministers resign over Brexit deal Anne-Marie Trevelyan Parliamentary private secretary in the Department of Education Anne-Marie Trevelyan resigned stating that she cannot support the deal Cabinet ministers resign over Brexit deal Handout image taken from the Twitter feed of @annietrev of the resignation letter addressed to Prime Minister Theresa May from Anne-Marie Trevelyan, a parliamentary private secretary in the Department for Education. PRESS ASSOCIATION Photo. Issue date: Thursday November 15, 2018. Ms Trevelyan has resigned saying she cannot support the Brexit deal after negotiations âbuilt on the UK trying to appease the EUâ. See PA story POLITICS Brexit. Photo credit should read: @annietrev/PA Wire NOTE TO EDITORS: This handout photo may only be used in for editorial reporting purposes for the contemporaneous illustration of events, things or the people in the image or facts mentioned in the caption. Reuse of the picture may require further permission from the copyright holder. PA Cabinet ministers resign over Brexit deal Sam Gyimah Universities minister Sam Gyimah resigned on November 30, claiming the government's decision to pull out of the EU's Galileo satellite navigation system as a deciding factor PA Cabinet ministers resign over Brexit deal Shailesh Vara Shailesh Vara who has quit as Minister of State for Northern Ireland, saying he cannot support Theresa May's Brexit agreement, which he said "leaves the UK in a halfway house with no time limit on when we will finally be a sovereign nation" PA Cabinet ministers resign over Brexit deal Cabinet ministers resign over Brexit deal Suella Braverman Brexit minister Suella Braverman has resigned, stating “It is not what the British people, or my constituents, voted for in 2016.” Cabinet ministers resign over Brexit deal Ranil Jayawardena Parliamentary private secretary to the ministry of justice Ranil Jayawardena resigned as he could not back the deal "in good conscience"

He added: “Having considered the amendment and spoken to a number of [MPs], I’m happy to confirm that the baseline for this comparison will be the status quo that is today’s institutional arrangements with the EU.

“The analysis will consider a modelled no-deal scenario on World Trade Organisation terms, a modelled analysis of a [free trade agreement] scenario and a modelled scenario of the government’s proposed deal, and in each case these will be compared against the status quo of the current institutional arrangements within the EU.”

However, he dismissed calls for the Office for Budget Responsibility to publish an independent assessment of the accuracy of the government’s analysis, saying this was beyond the watchdog’s remit and would set an “undesirable precedent”.

Previous leaked documents suggest the government’s analysis is likely to show that remaining in the EU would be better for the economy than Ms May’s proposed deal.

Anti-Brexit MPs hope to ramp up the pressure for a fresh referendum after Ms May admitted that Brexit could still be stopped. They will consider it a major victory that the prime minister’s proposed deal will be officially compared with the potential merits of staying in the EU and not merely considered against the risks of a no-deal Brexit.

Mr Umunna said the amendment could “change everything”.

Writing exclusively for The Independent, he said: “In a big admission – given she has been peddling, for many weeks, the falsehood that the choice is between her deal and no deal – the PM conceded in the House of Commons last week that the country actually faces three choices: no Brexit; no deal; or her agreement.

“Therefore it is only right that MPs are provided with an economic analysis with a comparison between those options. Anything less would amount to pulling the wool over the eyes of parliamentarians and the people we represent.