Britain's Chancellor of the Exchequer Rachel Reeves speaks about her plans for Britain's economy in Eynsham, England, Wednesday Jan. 29, 2025. Britain's Chancellor of the Exchequer Rachel Reeves speaks about her plans for Britain's economy in Eynsham, England, Wednesday Jan. 29, 2025. 

Rachel Reeves is already facing a major backlash within her own party after giving the green light to plans for a third Heathrow runway.

In a major speech today, the chancellor announced the expansion of the country’s busiest airport, saying the UK “cannot duck the decision any longer”.

She added: “A third runway would unlock growth, boost investment, increase exports and make the UK more open and more connected and now the case is stronger than ever.”

It’s part of the government’s wider pledge to boost economic growth after a turbulent few months for the country’s finances.

But the prospect of a third Heathrow runway has opened up a major split within the Labour Party, with opponents of the project saying it is at odds with the government’s pledge to reach net zero carbon emissions by 2050.

The Labour mayor for London, Sadiq Khan, immediately came out swinging after Reeves’ announcement.

He said: “I remain opposed to a new runway at Heathrow airport because of the severe impact it will have on noise, air pollution and meeting our climate change targets.”

Khan said he would “scrutinise” the details of the third runway plan when they are eventually published.

But he added: “I’m simply not convinced that you can have hundreds of thousands of additional flights at Heathrow every year without a hugely damaging impact on our environment.”

Asked about the mayor’s comments, a spokeswoman for the PM said: “We look forward to working with the mayor throughout the process.”

She added: “These proposals are consistent with our climate obligations.”

Khan was not the only opponent to the proposals, though.

John McDonnell MP, who was suspended from the Labour Party in the summer for voting against the government’s two-child cap policy, wrote on X: “This is such a huge political, economic and especially environmental mistake that sadly I fear it will inflict an irreparable scale of damage on the government.”

Another suspended Labour MP, Zarah Sultana, pointed to Starmer’s own record as she confirmed she was against the idea.

She said: “In 2018, the prime minister opposed a third runway at Heathrow.

“Now, in the middle of a climate emergency, his government is backing it. A complete U-turn at the expense of local communities and the planet.

“Reckless, short-sighted and indefensible.”

Former shadow climate change secretary and current Labour backbencher Barry Gardiner even called the chancellor “an environmental illiterate” for her “totally irresponsible” decision.

Speaking to PoliticsHome, he said: “The mistake the chancellor is making is to pit decarbonisation against economic growth. For the past several years, the Labour Party, she and Keir Starmer, have been insisting correctly that future growth depends on the journey to net zero. They have now completely done a U-turn.”

Labour MP and the transport committee chair Ruth Cadbury also told the outlet on Tuesday that she had “doubts” about how the airport would be expanded while making sure the UK does not lose sight of net zero commitments.

She added: “Even if we open a third runway, even if it delivers good growth, it won’t happen for 10 years at the absolute minimum, would you not want to see some growth sooner?”

Reeves also faces cabinet opposition to the plan, with energy secretary Ed Miliband, environment secretary Steve Reed, culture secretary Lisa Nandy and Northern Ireland secretary Hilary Benn all voting against it in the past.

Reeves’ deputy Darren Jones, the chief secretary to the Treasury, as well as her own sister, Labour chair Ellie Reeves, and development minister Anneliese Dodds have also opposed it in the past.

But it looks like they are all following the government line – for now.

There is some support for the idea among the unions, many of whom lobbied in favour of the airport expansion in 2016.

Unite general secretary Sharon Graham described it as “positive news”.

But she warned: “A third runway at Heathrow must be about more than just infrastructure – it’s about investing in the workforce and securing the future of good, unionised jobs.

“With workers facing economic uncertainty, these projects must deliver real opportunities for highly-skilled, well-paid employment that puts money back into working families and local communities.”

Community assistant general secretary, Alasdair McDiarmid, said it would “bring significant economic benefits” to the UK, and a “generational opportunity for UK-based steel procurement”.

Similarly, the Trades Union Congress (TUC), which is not affiliated with the Labour Party, seemed on board.

General Secretary Paul Nowak said: “Plans for a new third runway at Heathrow must deliver thousands of high-quality jobs across the country and boost UK supply chains. They must also ensure that our legal obligations on net zero can be met.”

And some backbenchers also sided with the government, including Labour MP for Hemel Hempstead David Taylor who wrote on X: “I welcome these bold plans!”

Luckily for Reeves, her MPs’ loyalty will not be put to the test over this issue anytime soon, as the decision on whether to back the expansion does not need a vote in the Commons having already passed in 2018.