Boris Johnson and Liz Truss have launched a challenge to Rishi Sunak’s authority by joining a Tory rebellion backing wind farms to tackle the energy crisis.
In their first major interventions since leaving Downing Street, the two former prime ministers have demanded an end to the ban on new onshore wind farms.
They both signed an amendment to the Government's Levelling Up and Regeneration Bill, just days after Mr Sunak’s government was derailed by a separate Tory revolt on the same legislation.
The bill is designed to speed up housebuilding, which is crucial to Mr Sunak's growth agenda.
The two former prime ministers have had tense relationships with Mr Sunak.
Mr Johnson's supporters view Mr Sunak as having dealt the fatal blow to his premiership by resigning as chancellor.
Ms Truss and Mr Sunak clashed repeatedly during the leadership race.
It is unusual for former leaders to oppose their successors, with Theresa May choosing the issue of partygate to make a rare criticism of Mr Johnson.
'We should seize the moment'
Mr Johnson signed the pro-onshore wind amendment, tabled by Simon Clarke, who was levelling up secretary under Ms Truss - even though he supported the ban, which has been in place since 2015, during his three years in office.
Ms Truss said she wanted to end the ban when she was in Number 10, because she believes the energy crisis means Britain needs more energy independence.
Mr Clarke told The Telegraph on Thursday: “I’m very grateful to all the colleagues from right across the Conservative Party who have put their names to this amendment, and especially Boris and Liz.
“Onshore wind is the cheapest form of energy generation open to us and is right for both our energy security and the environment.
“My amendment means it would only be possible for this to proceed where there is express community consent, with no right of appeal for developers if a council says no.
“I am strongly of the view that we should seize the moment - not least because a future Labour government wouldn’t include equivalent community consent protection were they to scrap the current ban, as they undoubtedly would.”
The onshore wind revolt is the second blow to Mr Sunak's bill.
On Tuesday night, more than 50 Conservative MPs rebelled against his plans to impose centrally-dictated housebuilding targets - forcing the Prime Minister to delay the votes until December.
That revolt risked the prospect of Mr Sunak only being able to get the measure through with Labour support.
The latest rebellion looks set to be even more serious - not only because it has attracted the support of two former prime ministers, but because it is considered more likely that Labour would back measures to promote onshore wind.
By Thursday night, a total of 18 Conservative MPs had signed the amendment.
It demands that Michael Gove, the present Levelling Up Secretary, revises the National Planning Policy Framework to allow councils to grant new onshore wind applications.
The amendment would also force the Town and Country Planning Act to be amended to allow the installation of “new onshore wind sites not previously used for generating wind energy or for repowering existing onshore wind applications”.
Onshore wind is a touchstone issue for the Tories.
Complaints from residents in areas they were constructed, often rural Conservative constituencies, have led the party leadership to take a critical stance.
In 2014, David Cameron said that the public were “fed up” of the turbines and promised not to subsidise them if the Conservatives won the upcoming general election.
The 2019 Conservative manifesto mentions growing offshore, but not onshore, wind.
Boris Johnson 'almost served in Liz Truss's cabinet'
News of the rebellion - just a month after Mr Sunak entered Number 10 - comes as a new book by journalist Sebastian Payne, The Fall of Boris Johnson, claimed that Mr Johnson almost served in Ms Truss’s cabinet as foreign secretary.
Ms Truss met the former prime minister twice during this summer’s leadership contest, Mr Payne revealed.
The pair also spoke on the telephone in the last week of July - when Mr Johnson was still prime minister, where they in effect discussed a job swap should she win the contest.
She suggested that he could return to the Foreign Office, where he had served from 2016 to 2018, to concentrate on the war in Ukraine. But in the end, the pair decided such an arrangement would be too complicated.
Ms Truss and Mr Johnson also had breakfast in Mr Johnson’s Downing Street flat on July 29.
Her allies said he gave her plenty of “good advice”, which was followed up by a later visit to Chequers with political thoughts on the campaign.
The book revealed that such invitations were not extended to Mr Sunak.
Both Mr Sunak and Ms Truss were asked repeatedly during the leadership campaign whether they would offer Mr Johnson a position in their government.
At one debate, Ms Truss said: “I very much suspect he would not want a future role in government, he needs a well-earned break.
“I’m sure he will have a role, I’m sure he will be vocal but he won’t be part of the Government.”
Mr Sunak said: “The simple answer for me is no. We need to look forward at this point, we need to bring change that people need.”
Despite their discussions about a job offer, earlier this week Mr Johnson compared Ms Truss’s mini-Budget to a badly-played piano, in a reference to a Morecambe and Wise sketch.
The Telegraph can also reveal that Ms Truss is planning to stand at the next election to continue her career as a Conservative MP despite being ousted from Number 10, according to former aides.
Ms Truss is understood to have rejected following the approach taken by Sir Tony Blair and Mr Cameron, who left Parliament swiftly after announcing their resignations.
Instead, Ms Truss is seeking a post-No 10 career more in line with Theresa May, who continues to speak regularly in the House of Commons five years after stepping down as prime minister.
Tory MPs have been urged to decide before Dec 5 whether they plan to compete for their seat again at the next general election, expected in 2024, or step aside.
Chloe Smith, the former work and pensions secretary, and William Wragg, the vice-chairman of the 1922 Committee of backbench MPs, both announced this week they will not run at the next election.
There has been speculation that as many as 80 of the current crop of almost 360 Tory MPs could choose not to seek re-election.