Mr Johnson, 41, will today signal that he is prepared to step down as editor of the right-wing Spectator magazine if, as expected, his fellow Old Etonian David Cameron wins the battle to lead the Conservative Party.
In the latest chapter of his colourful personal and professional life, Mr Johnson appears to have accepted he can no longer moonlight as a journalist and politician, revealing that his lust for power has eclipsed his desire to be a high-profile editor.
With supporters confident that Mr Cameron will win the battle to become the new Tory leader, Mr Johnson will tell Sue Lawley on today's Desert Island Discs programme that he "would choose politics" over journalism when the moment was right.
Mr Johnson, whose regular appearances on shows such as Have I Got News For You have made him the most popular Tory figure among young voters, says in the pre-recorded programme: "All politicians are like crazed wasps in a jam jar, each individually convinced that they are going to make it."
He adds: "My ambition silicon chip has been programmed to try to scramble up this ladder, so I do feel a kind of sense that I have go to do [it]."
Andrew Neil, the former Sunday Times editor who is now Mr Johnson's boss at The Spectator, last night told The Independent on Sunday he was not surprised by the news. "I had been half expecting it," he said.
Mr Neil added: "I am on record as saying that I believe that being an editor is incompatible with being in the Shadow Cabinet. I have said as much to Boris and he agrees. I think it's on the margins about whether you can be an MP and an editor, but Conrad Black [the previous owner] had allowed it, so I let it go."
Mr Johnson and Mr Neil have had an increasingly uneasy relationship since a series of scandals erupted at The Spectator, which was dubbed the "Sextator" on account of the number of affairs to begin at the magazine's Doughty Street offices, including that of publisher Kimberly Quinn - who had a relationship with the then Home Secretary, David Blunkett.
After Mr Neil reputedly instructed his editor to carry more news specials recently, Mr Johnson promptly published a 3,000 word article in The Spectator about the Roman poet Horace, musing on the pivotal role of the battle of Actium, under the headline: "Investigation".
Until now, Mr Johnson has managed to keep the two careers in politics and journalism running in tandem since he was first elected to Parliament in 2001. "I think I have successfully ridden two horses for quite a long time, but I have to admit there have been moments when the distance between the two horses has grown terrifyingly wide, and I did momentarily come off," the Henley MP tells the BBC Radio 4 programme.
The most high-profile clash of interests between the twin roles came with an explosion of fury on Merseyside when a Spectator editorial accused Liverpool of wallowing in its "vicarious victimhood" after the execution of the hostage Ken Bigley in Iraq.
Although he had not written the piece, Mr Johnson accepted responsibility and was forced to visit the city to make a grovelling apology. The furore proved that combining a frontbench job with an editorial chair was "ludicrous", he admits in today's interview.
"The poor old Tory Party - the wonderful old Tory Party - was in the ghastly position of having to agree with everything in the editorials of The Spectator by virtue of the fact that I was on the front bench."
His departure from The Spectator will end an 18-year career in journalism. It did not start well. He was sacked as a trainee reporter for The Times in 1987 for falsifying a quote from his godfather. But after a spell at The Express and Star in Wolverhampton, he found a home at The Daily Telegraph, a paper in tune with his outlook and breeding, as the son of a former Tory MEP. He was assistant editor for five years before leaving to edit The Spectator in 1999.
After six years as editor, - four while an MP - Mr Johnson was forced to resign as Michael Howard's arts spokesman after he described allegations that he had had an affair with writer Petronella Wyatt as "an inverted pyramid of piffle". Ms Wyatt later confirmed their relationship and Mr Johnson was dismissed for the apparent dishonesty rather than the relationship.
The Spectator's new owners, the Barclay brothers, were understood to be unamused by the goings-on.
Among names suggested to replace Mr Johnson as editor is Geordie Greig, of the society magazine Tatler. Mr Greig said last night he did not wish to comment.
Life and crimes of Johnson
1987: Joins The Times after Eton and Balliol College, Oxford. He is sacked as a trainee reporter after making up a quote.
1997: Stands as Tory candidate in Clwyd South. Loses.
1999: Appointed editor of The Spectator.
JUNE 2001: "Go back home and prepare for breakfast," he tells Tories after being elected to serve the constituency of Henley.
JUNE 2004: "My chances of being PM are about as good as the chances of finding Elvis on Mars."
OCTOBER 2004: Sent to Liverpool to apologise for accusing city of "wallowing" in "victim status".
OCTOBER 2004: "An inverted pyramid of piffle" is Johnson's description of allegations that he had an affair with Spectator columnist Petronella Wyatt. Later sacked by Michael Howard for denying the affair.
APRIL 2005: "Voting Tory will cause your wife to have bigger breasts and increase your chances of owning a BMW M3," he declares.
APRIL 2005: Indicates his grasp of Tory policy. "I can't remember what my line is on drugs. What's my line on drugs?"Reuse content