One was a contemporary of David Cameron at Eton and Oxford, the other is a self-educated, working-class Londoner who missed out on university.
As well as a shared surname, Boris Johnson and Alan Johnson could soon have something else in common – candidacy for the job of Mayor of London. Alan Johnson, the former home secretary, is being urged by colleagues to put himself forward in the mayoral election of May 2012, when it is likely the coalition government led by Mr Cameron will be suffering mid-term unpopularity, making the Conservative Mayor, Boris Johnson, vulnerable to a strong Labour challenger.
In 2008, Boris Johnson beat the Labour incumbent, Ken Livingstone, by 1,168,738 votes to 1,028,966 at a time when the Labour government was suffering a slump in its support. A Johnson v Johnson contest would appeal to the organisers of the Labour campaign.
Labour's Alan Johnson was brought up by his teenage sister in a tenement in Notting Hill after his mother's early death, and was educated at a grammar school in Chelsea. His father was a painter and decorator, and he went to work at 18 as a postman. But before he could take on the other Mr Johnson, he would need to persuade members of the London Labour Party to vote for him to be their nominee in preference to Mr Livingstone, who is known to want his old job back.
Alan Johnson's age may be a disadvantage because he will be close to his 62nd birthdayin 2012, and would be running against an incumbent 14 years younger. However, he is nearly five years younger than Mr Livingstone.
Mr Johnson had considered putting himself forward for the leadership of the Labour Party, which he would have had a strong chance of winning had another general election looked likely within a few months. He ruled himself out after the Conservatives and Liberal Democrats struck a deal to delay the election until 2015. A former close associate of Mr Johnson said: "He wouldn't dismiss [the chance to become Mayor], because he is a Londoner through and through, he cares deeply about the capital, and the election is on the alternative vote system. Voting reform is one of his main priorities."