The frictions between Tony Blair and John Prescott are chiefly a result of the two men's very different backgrounds and political traditions. These lie at the root of this week's barely-veiled row about public-sector workers.
There have been uneasy pairings at the pinnacle of government throughout modern history. Relations between Harold Wilson and George Brown in the 1960s were famously stormy, as had been those between Harold Macmillan and Rab Butler.
Not all prime ministers bother to appoint a deputy and the title has no constitutional basis. Indeed, the nebulous nature of the job accounts for some of its problems; the office is what the holder makes, or is allowed to make of it.
When Margaret Thatcher grudgingly appointed Geoffrey Howe her second- in-command in 1989, as a consolation prize for losing the foreign secretaryship, she made it clear that it was a courtesy title.
In the circumstances, it was not surprising that things ended so badly. Goaded beyond endurance by his leader's strident hostility to Europe, Sir Geoffrey made a vitriolic resignation speech in which he described her as a cricket captain who sent out her players with a broken bat.
How she must have yearned at that moment for Willie Whitelaw, her ultra- loyal deputy for nearly a decade, despite having been defeated by her in the 1975 party leadership election.
Michael Heseltine called Lord Whitelaw the "rock" of Lady Thatcher's Cabinet. It is unlikely that John Major would say the same of Mr Heseltine, whom he made his deputy in 1995 after surviving a leadership challenge - but not, the two men always claimed, as a reward for Mr Heseltine's support. Whether there was a deal or not, Mr Heseltine frequently took the opportunity to undermine Mr Major, particularly on Europe.
It is often said that the appointment of a deputy is an attempt to neutralise a rival. As Mr Major discovered and Mr Blair may be starting to realise, the plan does not always work out.