The public has so far shown remarkable tolerance of David Blunkett’s behaviour. As today’s Populus poll in The Times shows, less than half the public views the allegation that the Home Secretary has had an affair with a married woman as serious. Fewer than one in five believes it should be a resigning matter. The findings reflect a significant shift in public attitudes, with half of voters now believing that politicians’ private lives are irrelevant.

When allegations of misdemeanours enter the public sphere, however, sympathy falters. The alleged misuse of his position to help Kimberly Quinn’s nanny to get a visa to stay in Britain, and the use of a free parliamentary rail pass for Mrs Quinn, are seen by the public as serious matters. Even these, however, are not considered grounds to resign by the majority. This may reflect the peculiar degree of public affection for the Home Secretary, a view shared by the Prime Minister who considers Mr Blunkett one of the few ministers able to cut through the political static and reach voters whom others cannot impress. The Home Secretary’s triumph over adversity has given him an appeal to which other public figures can only aspire. Voters appear willing to overlook indiscretions which in others would be deemed reprehensible . . . for now.

For whatever the present view of the public, the fate of the Home Secretary lies not in their hands, but with Sir Alan Budd, who is reviewing Mr Blunkett’s behaviour. Sir Alan must consider the allegation deemed most serious by voters: that of the fast-tracked visa application. The less important but more salacious details surrounding the Blunkett affair have overshadowed some of the more basic questions about this matter.

Simply asserting, as allies of the Home Secretary have done, that any fast-tracking was done without Mr Blunkett’s knowledge, is not good enough. Mr Blunkett must explain why he enlisted the help of a senior civil servant to read the application form. Were it simply a matter of reading it out loud, then surely Mrs Quinn, or a friend not connected to the Home Office, could have done that for him? There is uncertainty, too, over whether Mr Blunkett merely “looked over” the initial application form or whether, as Mrs Quinn assserts, he took the matter up once the nanny had been officially informed that she faced a year’s delay — a decision remarkably overturned within three weeks.

Either way, blaming an overzealous official for fast-tracking the application would be not only ungracious and cowardly, but also dishonest. A man holding one of the great offices of state must exercise extreme caution over putting himself in situations in which his position can be compromised. The decision to use civil servants to intervene in and give advice upon Mr Blunkett’s private life was also highly questionable. This episode may yet come down to a question about the Home Secretary’s judgment. Incautious but sagacious remarks about fellow Cabinet ministers made to his biographer Stephen Pollard, and published for the first time yesterday, hardly confirm Mr Blunkett’s reputation for political discipline.

British public life is remarkably clean by international standards. It is to the credit of the nation that an inappropriate intervention over a nanny’s visa application may still amount to a ground for dismissal or resignation. But, undoubtedly, it may.