He is ambitious, has a populist style, a way with words that can make a soundbite seem unintentional, plays the electric guitar and once wanted to be a rock star.

Sounds familiar? Frighteningly so. Particularly to the man in No 11 Downing Street, who can imagine nothing worse than having him move in next door.

The fact that Alan Johnson could even blush when asked last week if he envisaged taking on Gordon Brown for the Labour party leadership was almost engaging, as if — heaven forfend! — the idea had never even entered his head.

If he should have greatness thrust upon him — or even the chance to “have a pop at” greatness, as he might say himself — he looks increasingly unlikely to pass up the opportunity. The job he just two years ago described as “science fiction, but nice science fiction”, may still be beyond his grasp, but it no longer looks like reaching for the stars.

Johnson as a potential challenger has the advantage of being a southern Englishmen whereas the alternative leading contender, John Reid, is another Scot. He also appears to be a paid up member of the human race; a cheeky, chirpy meritocrat to cheer those bored by the chancellor’s gloom and the prime minister’s histrionics. The member for Hull West and Hessle, is loyal to Blair, ruthless and shrewd.

For the moment he is keeping his counsel but when, no longer “if”, Tony Blair steps aside during the next 12 months to make way for an older man, the odds are shortening on Johnson as frontrunner for the “anyone but Gordon” camp. Shortening on a daily basis, in fact: from 5-1 to 11-4 in the past week. Brown (2-7 lengthening to 4-9) is still the favourite but no longer looks quite such a shoo-in. David Cameron’s successful run for the leadership against the favourites is a good omen.

If Johnson’s rise to prominence seems meteoric, that’s because it is, not least because he started from the lowest level. Johnson is the nearest thing new Labour has to a genuine working-class hero. He is not given to bragging about it on the inverse snobbery circuit, however: “My working-class credentials are impeccable, although I don’t get them out and polish them every five minutes,” he once told The Guardian.

Yet he is unquestionably the most visible example of a pulled-up-by-his-own bootstrings politician our supposedly classless society has produced since, oh . . . John Major. Although perhaps that’s not the analogy his supporters most want to hear right now.

Johnson was born in 1950 in the part of Chelsea where the natives rarely refer to it as the “royal borough”. Significantly, he remains a loyal Queens Park Rangers fan. His father, a painter and decorator, ran off when Alan was just eight and his mother died four years later.

He and his sister were destined for the local Barnardo’s but for the perspicacity of a local child welfare officer he remembers as Mr Pepper, who was so impressed with the nous of Alan’s sister, then 15, that he persuaded the local authority to give them a council flat in Battersea.

For the next three years young Alan made the daily trip across the river to Sloane grammar school back in Chelsea, where he was not exactly a model pupil.

While Brown was undergoing select tuition at Kirkcaldy high school in preparation for Edinburgh University, at the age of just 16 Johnson had left a school that was “glad to see the back of me” with no qualifications to join the other no-hoper wannabe rock stars roaming Chelsea in the mid-1960s. He joined a band and even cut a 7in single.

He quit a day job as a shelf-stacker in Tesco because they wouldn’t let him take a lunch break, his first introduction to what seemed the particularly one-sided world of employee bargaining.