Labour MPs who disagree with Jeremy Corbyn’s opposition to the expansion of Heathrow airport have been working closely with government ministers and Tory whips to ensure the plans win parliamentary approval on Monday, in an extraordinary show of defiance against their party leader.

The extent of behind-the-scenes cooperation with the government on such an important policy issue is believed to be unprecedented and all but guarantees that the third runway plan will be passed, despite Corbyn, his shadow chancellor John McDonnell and the Labour front bench opposing the move.

Sources in the rebel group said there had been “ongoing discussions with the government since January”, which have involved members of Labour’s backbench transport committee, to make sure the third runway was approved with the support of Labour backbenchers.

Talks have been continuing this weekend between the pro-expansion Labour MPs and the Tory whips, after Greg Hands, whose constituency lies under the Heathrow flightpath, resigned as international trade minister so that he could oppose the plans.

With a handful of other Tories including Zac Goldsmith and Justine Greening also expected to rebel, Hands’s resignation created jitters in the Tory whips’ office about the vote. Boris Johnson, the foreign secretary, another outspoken critic of the plans, will be out of the country for the vote.

A group of 40 Labour MPs, including the chair of the backbench committee, Gavin Shuker, today release a joint statement to the Observer spelling out why they will support the airport’s expansion. They say the plans meet all the tests on environmental and noise pollution and capacity, contradicting the party line. They believe that up to 100 Labour MPs will vote in favour.

Party sources said the Unite union, Labour’s biggest financial backer, approved the statement and was also urging other MPs to back expansion, saying it would be good for the economy and create jobs.

Facebook Twitter Pinterest Greg Hands resigned as a junior minister so he can oppose the expansion. Photograph: Niklas Halle'N/AFP/Getty Images

The statement says Heathrow expansion will create up to 180,000 new jobs. “As this project will span multiple parliaments,” the statement says, “– including, we hope, a Labour government – it’s our responsibility to secure strong cross-party backing for this project and can meet Labour’s tests on air quality and noise.” It argues that “the decision in principle is right: we urge our Labour colleagues to back Heathrow in parliament tomorrow.”

It is understood Labour MPs made clear to their whips and Tory business managers they would defy a three-line whip if imposed by Corbyn, and vote with the government. As a result Corbyn was forced to offer a free vote.

Shuker said: “This project will span more than one parliament so it’s vital that more than one party of government makes its support clear. The case for Heathrow has been proved: I expect a majority of backbench Labour MPs to back it.”

Earlier this month Baroness Sugg, the Tory aviation minister, addressed the backbench Labour transport committee about the Heathrow plans.

Andy McDonald, the shadow transport secretary, said earlier that Labour strongly opposed the plans. “Labour has always argued that airport expansion must meet our four tests. After careful and rigorous consideration, we are clear that they have not been met. Heathrow expansion is incompatible with our environmental and climate change obligations and cannot be achieved without unacceptable impacts on local residents.

“The improved connectivity to the regions of the UK cannot be guaranteed and there are unanswered questions on the costs to the public purse and the deliverability of the project.

“We support vital investment in our country’s transport infrastructure, but every investment must be tested on whether it provides real value for money and sustainability. A third runway at Heathrow fails this test.”

Separately the Labour MP Lucy Powell has organised a cross-party letter to transport secretary Chris Grayling, signed by 21 Greater Manchester MPs – including Angela Rayner, the shadow education secretary, and Graham Brady, the chairman of the 1922 committee of Tory MPs – expressing conditional support for expansion. The MPs say they are minded to support the third runway tomorrow but seek assurances from the government that it will deliver “an integrated transport plan for the Northern Powerhouse which brings together investment in rail, road and aviation infrastructure to enable us to work together to drive economic growth and rebalance our economy”.