Green Party strategists have identified these mothers, and some fathers, as a group of voters who are particularly concerned about the impact of climate change on their children and so may be open to switching to voting for the Greens.

London sweltering in the heat in August

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Many families living in Inner London had to endure the sweltering temperatures in flats or small houses without gardens and the greater open spaces in the capital’s suburbs.

The Green strategists believe they may be able to win over a sizeable number of mothers so worried about climate change that they have become “Green curious” - having previously shied away from the party because they did not want radical change.

But with the threat from global warming now so glaringly obvious and with unusually hot weather returning this week, Green Party campaigners have been turning up at schoolgates to engage parents about the issues concerning them ahead of the by-election on October 8.

The heatwaves and climate change have been regularly cited, particularly by mothers.

Mr Polanski told The Standard: "Like so many in London, I really struggled during the heatwaves this summer.

“People are telling me time and time again, that they want Labour to do more to help with this. To take the environment seriously.

“And that's what a Green vote in Holborn and St Pancras will do, it will force Labour to take Green issues seriously."

The Labour Government is strongly backing a third runway at Heathrow

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A Green source said: "The heatwave has propelled the environment up the list of concerns for voters - especially here in London.

“People can see Labour delaying decisions on more north sea oil and gas drilling, rowing back on climate spending and pushing ahead with airport expansion.

“They can see a party not taking the climate crisis seriously and this worries people, especially parents.

“This is especially true for Green curious former Labour voters.”

George Galloway who is the Workers Party of Britain’s candidate in Holborn and St Pancras

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But the Greens claim there is a shift to their party which could put the result on a “knife-edge”.