And yet, the scrawled pledge – “Dear Andrea, Delighted that you’re in our top three, Yours Boris” – never made it into the hands of the energy minister, who decided instead to stand herself.
Now the MP for South Northamptonshire, who entered parliament in 2010, has leapfrogged Michael Gove to become second favourite with the bookmakers to be the next Conservative leader and prime minister.
In her six years in parliament, Leadsom has notably irritated George Osborne, not once but twice. First, as one of the ringleaders of a Tory rebellion pushing hard for the prime minister to agree to an EU referendum, she refused to budge during a last-minute call from the chancellor, although she denies swearing at him down the phone.
Her support is now growing among MPs, some of whom see her as the best option among the Brexit backers, and others who see her as a way of preventing Gove from making it into the final two.
#Andrea Leadsom was widely expected to be a high-profile member of Team Boris, in a deal that was going to be secured via a handwritten note handed over at a Conservative summer party.