Zack Polanski has torn into the Labour Government’s full-blown support for a third runway at Heathrow, branding the project a “great betrayal”.

The Green leader unleashed his criticism of a bigger Heathrow as his party and Labour were both ramping up their campaigns for the Holborn and St Pancras by-election on October 8.

Mr Polanski told The Standard: “A third runway at Heathrow would be a great betrayal.

“A betrayal of our climate commitments, a betrayal of communities breathing polluted air, and a betrayal of our children’s future.”

Mr Polanski hit out after the Government’s own global warming advisers warned that there is “no credible pathway” for a Heathrow third runway within the UK’s legally-binding climate targets under current policies for cutting aviation emissions.

The UK’s Climate Change Committee (CCC) also stressed that the Government “does not have a credible plan to reduce” aviation emissions, posing a serious challenge to meeting overall global warming targets.

The advisers argued that expansion of Heathrow airport cannot go ahead unless the aviation industry is forced to clean up its climate emissions.

The cost of international flights might have to increase by hundreds of pounds by 2050, to pay for measures that will help the airline sector cut its carbon pollution to zero overall, known as net zero, the CCC said.

But Government minister Martin McCluskey appeared to brush aside the committee’s warnings.

“Look, I've got a lot of time and respect for the Climate Change Committee, but their advice is exactly that,” he said.

“It is advice.”

Earlier, Chancellor John Healey had given the Government’s backing to a third runway, which will cost an estimated £49 billion, once terminal area improvements, moving the M25 and other investment are included.

The new runway would increase the airport’s to 756,000 flights and 150 million passengers a year.

But Mr Polanski stressed: “The Climate Change Committee has told this Government plainly: there is no credible pathway for Heathrow expansion within our climate commitments under current policies.

“There is no more room for political fudge, no more pretending that you can pour more concrete, add more flights and somehow make the climate crisis disappear.

“And yet Labour is still trying to push this reckless project through.”

Prime Minister Andy Burnham has previously expressed concerns over the expansion, and it has long been opposed by climate experts and Mayor of London Lord Sadiq Khan.

Airlines have also warned that they and passengers face being left to pick up the bill for what they say is the most expensive new runway scheme ever.

A Heathrow spokesperson said: “Heathrow expansion cannot be a choice between economic growth and net zero – it must deliver both.

“The Climate Change Committee’s assessment does not change this and acknowledges that the key solutions exist today.

“We will continue working with Government and partners across the aviation sector to ramp up today’s proven technologies, while examining options for how the billions of pounds passengers already pay in carbon taxes can be used to support this.

“Given the right policies, a growing aviation sector can be empowered to deliver the huge economic and social value that air travel brings, while increasing pace of delivery of the solutions needed to accelerate aviation’s decarbonisation.”