Leading article: The lawyer, his wife, her job and their mortgage

Acruel fate decreed that the Culture Secretary, Tessa Jowell, should begin this week helping to launch a government report on women's work and pay. The association of women and money was probably the last thing that she wanted to be reminded of just then.

Ms Jowell faces a predicament that seems, at first sight, to be none of her making. A hard-working, well-liked and effective minister, she faces calls for an inquiry because of the professional activities of her jet-setting solicitor husband, David Mills. The only proven link between their financial affairs - which they both insist are kept separate - is her signature on a mortgage application they made on their London house.

This mortgage it turns out, however, was not just a mortgage. It provided a mechanism that allowed Mr Mills to bring a large sum of off-shore money into the country, no questions asked. How he came by this sum and by what convoluted route it reached the hedge fund that was its last resting place before it paid off the mortgage are questions that an Italian prosecutor is looking into. As well they might. Mr Mills's explanations so far have seemed bizarre and implausible in the extreme.

They would have remained questions for Mr Mills alone, however, had Ms Jowell not co-signed the application. Either, her critics say, she knows more than she is saying or, as an intelligent woman and competent minister, she certainly should have done.

A Cabinet minister cannot afford even the appearance of association with financial impropriety. Add the widespread perception, from the Bernie Ecclestone affair to Peter Mandelson, that New Labour politicians, up to and including Tony Blair, are more enamoured of worldly wealth than is decent for a party with its working-class origins, and it is obvious how damaging this affair could be. Even if Ms Jowell has breached neither the law nor the ministerial code, the combination of suspicion, envy and political opportunism already swirling around Westminster is potentially lethal.

There are complex issues here that are not only political. Where couples keep their financial affairs separate, how far is responsibility for individual wrong-doing shared? Should the sins of one partner be visited on the other? Is a politician wife her non-politician husband's moral keeper? It is more than 20 years since Geraldine Ferraro's US presidential aspirations were blighted by her husband's dubious business affairs. Would comparable activities by a wife bring the downfall of her politician husband?

The only way to clear the air may well be for the Cabinet Secretary, Sir Gus O'Donnell, to conduct an inquiry into whether the ministerial code has been broken, as the Conservatives have demanded. But it is ludicrous that responsibility for such investigations should rest with a senior civil servant - and ultimately with the Prime Minister. At least some of the party political sting might be drawn if the remit of the overall ethics watchdog, the Committee for Standards in Public Life, were widened so that it could consider individual cases.

For the time being, Ms Jowell has the support of Mr Blair, who sat next to her at yesterday's Downing Street event. She also has the backing of the Lord Chancellor, who said that she had been "a really good minister" and should stay in her job. As he must know, however, being a good minister and surviving in office are different things. There are two circumstances in which Ms Jowell would have no choice but to go: if she is found to be personally implicated in dubious financial practices or if she is perceived to have become a liability to the Government. This may be rough justice, but it is political reality.