Philip Hammond sent Boris Johnson a text message offering to back him as party leader within hours of the General Election, it was claimed last night.
The scale of plotting to replace Theresa May is revealed in a new book, which claims Mr Johnson's leadership hopes floundered when it emerged she was not intending to step down.
But in the last few days the two Cabinet Ministers have been locked in a bitter feud over Brexit, with the Chancellor said to be furious at Mr Johnson's claims that his provocative 4,000-word article had forced a change of approach.
A war of words between the two senior figures threaten to undermine the fragile unity within the Cabinet which appeared to have been achieved shortly before the Prime Minister's speech in Florence on Friday.
The Chancellor is reported to have offered his backing for the leadership in a 4am text message to Mr Johnson on 10 June, as the reality of a hung Parliament had become clear, according to the Sunday Times political editor Tim Shipman.
An alliance between Mr Hammond, who has been pushing for a soft Brexit, and the Foreign Secretary, could have brought the Prime Minister down, but David Davis and Amber Rudd were also said to be preparing leadership bids.
A source, who discussed the leadership with the Chancellor, said he wanted David Davis "to run Brexit, (Hammond) could run the economy and Boris could run the shop" - but Mr Davis would not defer to Mr Johnson.
According to the account, an ally of Mr Hammond said: "I know on that first day he thought Boris could be the answer because he'd have this reach and appeal." A source close to Mr Hammond did not dispute the claim.
Mr Johnson was widely reported to be planning a run at the leadership after the election humiliation, until Mrs May announced she would be staying on.
But the book, Fall Out: A Year of Political Mayhem reveals Tory moderates including ex-prime minister David Cameron and George Osborne were rallying around Amber Rudd, the Home Secretary.
Allies of Mr Davis were said to have compiled a list of MPs who wanted Mrs May to step down some weeks later, after what was seen as her poor handling of the Grenfell Tower tragedy.
Tory MPs now expect Mrs May to stay on to oversee Brexit, but she will have to control her warring Cabinet Ministers.
Mr Johnson's camp claimed his article in the Daily Telegraph last week, seen as a leadership bid, had bounced the PM into reducing the transition period from five years to two, the Mail on Sunday claimed.
Allies of Philip Hammond responded furiously to the suggestion, calling it "total bull****".
One said: "I f****** hate having to deal with Boris on this level. What a shame he feels the need to do this.
"He is surely not suggesting that his article altered policy which had been worked up for months? The Chancellor has always been in favour of a two-to-three year transition."
At a two-and-a-half hour long Cabinet meeting last Thursday, senior government members were shown the text of Mrs May's speech in which she called for a two-year transition period after Britain leaves the EU in March 2019.
She also asked European leaders for a "ambitious economic partnership" between Britain and the EU after that period ends in 2021, which is not modelled on any previous agreements such as those with Canada or Norway.
Mr Johnson's ally told the Mail on Sunday: "The Treasury originally wanted up to five years and Hammond was pushing for four years recently. Before (Johnson's) article we were heading towards a Norway model - now we end up leaving completely."
The Chancellor and Foreign Secretary made a show of leaving the Cabinet meeting together on Thursday and sat side-by-side in the audience in Florence to applaud Mrs May.
But behind closed doors, Mr Hammond is reported to have "rolled his eyes" at comments by Brexiteers during Thursday's meeting.
The two are also at loggerheads over the rules of the transition period, with Mr Hammond understood to been for the status quo to continue, but Mr Johnson pushing that rulings from Brussels during this period should not apply.
As the party tries to paper over its divisions at their annual conference in Manchester next week, one Cabinet Minister told the Sunday Express that Mrs May was "in a dangerous place".