"It's a very nice place, Dorneywood," said Mr Johnson, who used a GMTV interview to put himself in the frame for the position of Cabinet number two, should the gaffe-prone Prescott fall on his sword. "I only went into the servants' quarters to deliver the mail but it looked very nice from the outside."
If Tony Blair thought his recent cabinet reshuffle (which elevated Mr Johnson to the top education job) would temporarily silence Westminster whispers over who wants who's job, he was deeply mistaken.
Mr Johnson's TV admission - the first time in 12 years that a senior Labour politician has explicitly expressed a desire for a top cabinet post - kicked off some of the most fevered media speculation since Wayne Rooney fractured his foot.
Other names were quickly added to that of the ex-trade union boss: Jack Straw, Peter Hain, Patricia Hewitt and Harriet Harman. But, in World Cup week, Mr Johnson quickly emerged as the firm favourite.
According to the Daily Telegraph and the FT, he is a shoo-in with odds of 6-4, and the Daily Mail was similar assured by offering 7-4 on Mr Johnson no longer using the tradesman's entrance to get into Dorneywood.
But most papers were not prepared to simply speculate over his candidacy for deputy PM. "Johnson should not be taken at face value when he protests that the deputy leadership is the limit of his ambition," wrote John Rentoul in the Independent on Sunday, saying he has now emerged as Gordon Brown's biggest challenger for the Labour leadership.
Right-wing commentators, in particular, were quick to trumpet Mr Johnson - the ultimate "Jack the Lad" - for the top job. Matthew Parris, the former Conservative MP, wrote in the Times that he was "clearly ambitious, but seems like a human being". The Spectator, in its own profile, even used the headline: "Alan Johnson is the Labour leader that Cameron's Conservatives fear."
But while some championed Mr Johnson, it was left to one of his own to question his loyalty to the working class. Writing in the Observer, Roy Hattersley, a former Labour deputy leader, painted Mr Johnson as a self-serving political chameleon who had refused to acknowledge the debts faced by poor students as a result of university top-up fees (which he helped engineer as higher education minister).
"Questions have to be asked about how much he remembers about his impoverished youth," Mr Hattersley said. But, whatever you think of Mr Johnson, rest assured the postman jokes are here to stay. Here's one you can expect to hear over the coming months:
"Who's there? "