The Green Party has called Heathrow’s expansion the “definition of irresponsible”, with the party’s co-leader, Adrian Ramsay, saying it was a “fantasy” that the projects could be done without environmental damage.

Reeves was questioned over her previous opposition to the expansion of Leeds-Bradford airport over air and noise pollution grounds.

“If Leeds-Bradford came back with plans to expand I would support these because I think things have changed significantly in the past few years,” she said.

She said there were now more efficient plane engines and the use of sustainable aviation fuel was a “game changer”.

However, supplies of this fuel are currently very low. According to the European regulator EASA, they made up just 0.05% of the fuel used in the EU in 2020. It also costs much more than regular jet fuel.

The UK government has introduced a Sustainable Aviation Fuel Mandate, external which stipulates that 2% of all jet fuel supplied this year must be SAF, increasing to 10% in 2030 and 22% in 2040.

The director-general of the International Air Transport Association, Willie Walsh, has cast doubt on how quickly this can be achieved.

“Sustainable fuel is a real thing, but we need it in significantly greater volumes than are available today,” he told LBC on Wednesday.

“Mandating airlines to use a fuel source that doesn’t exist today doesn’t make an awful lot of sense.”