Boris Johnson is being urged by Tory MPs to reconsider his “electorally toxic” planning reforms which they blamed for last week’s surprise Chesham and Amersham by-election defeat.

Boris Johnson

The Liberal Democrats took the Buckinghamshire seat for the first time in its history, winning a majority of 8,028 over the Tories on a spectacular 25% swing.

Voters’ concerns over the prime minister’s liberalisation of planning laws were cited by Tory MPs and activists as the primary reason behind the defeat.

Johnson pledged to “transform the sclerotic planning system” in England after becoming prime minister. He has promised to force all councils to rewrite their local development blueprints and deliver 300,000 new homes a year by 2025.

As part of the plans to boost the supply of new build homes, every local authority will have to designate land for either development or preservation.

But while the reforms are supported by the majority of Conservative MPs in the north of England and Midlands, Johnson faces a rebellion from those in southern counties, including the former prime minister Theresa May.

The revolt, which is being organised by Theresa Villiers, the former environment secretary, is believed to include around 50 MPs.

While they are not opposed to more housebuilding, they do reject the proposed use of a computer algorithm to decide how many homes should be absorbed by each area.

Bob Seely, the MP for the Isle of Wight who opposes the proposed reforms, said the Chesham and Amersham by-election result showed that “a bad planning bill is now electorally toxic in Britain, therefore it is critical we get it right”.

He wants the algorithm re-examined and more consent given to individuals.

Lib Dem leaflet

“Instead of a ‘developers’ charter’, we need a community-led solution. Communities are happy with more development when you give them a say in what is happening in their area,” he said.

The Lib Dems handed out anti-planning reform leaflets during the Chesham by-election, which clearly managed to resonate with voters.

The leaflets featured quotes from Theresa May and Iain Duncan Smith criticising the reforms.

Tory MP, Sir Roger Gale, says the by-election defeat was a “wake up call” for the prime minister amid a significant backbench rebellion over the plans.

He believes Johnson’s planning reforms have been left in “tatters” following last week’s result in Chesham and Amersham.

Gale told HuffPost that on Tory WhatsApp groups on Friday “the only thing anybody is talking about is planning”.

“The common theme is ‘me too, me too, me too’ – right across the south of England,” he said.

“They are worried about the policy,” he added. “But of course, they’ve got an eye on their re-election chances.”