Today Gordon Brown has defended John Prescott, under pressure because the press have reported that he has been unfaithful to his wife - conducting an affair with a secretary.
The chancellor has offered the usual line of defence in these instances, "its a purely private matter". But is that actually the case? I think that personal relationships are indeed private, and usually nothing to do with the press or the public. However the situation is different when it involves marriage. Marriage is not a private matter - but a public contract, made before witnesses and the law (and frequently invoking God too). Whether someone has honoured or dishonoured a public commitment can be many things -but surely not "private".
That is not to say that someone who has erred cannot continue in public office; history tells us that many great statesmen's personal lives were less than exemplary. What it does mean is that "he is doing a good job" is a reasonable line of defense to try to advance, as a person can be judged on their record. However when it comes to marriage, "it's a private matter" just doesn't work.