Melanie McDonagh: Do they have love rats in the non-judgemental party?

Can a Lib Dem be a love rat? I am thinking, of course, of John Hemming, the newly elected MP for Birmingham Yardley, who has announced that his long-standing personal assistant, Emily Cox, 27, is expecting his baby. No surprises there, then, but remarkably, Mr Hemming, 46, is not leaving his wife, Christine, also 46, mother of his three children. Indeed, they gave a press conference on Friday to announce that they were staying married, with Mr Hemming cuddling the family cat for the photocall - less exploitative than bringing in the children, don't you think?

Naturally, for anyone whose political memory goes back beyond 1997, there is a glow of déjà vu about this display of family solidarity. However, it was mostly Tories who went in for it - not the adultery with a younger woman, but the announcement from the erring husband that he was staying with his wife and from the wife that she was standing by the husband. The most celebrated Lib Dem to go through this routine was, of course, Paddy Ashdown, who also had a fling with his personal assistant, but I seem to recall that Mrs Ashdown left him to face the photographers alone. That affair was redeemed not only by Mr Ashdown's penitence but by the fact that the secretary looked even less like a floozie than Mrs Ashdown.

This scandal has emerged six whole weeks after the election, even though the relationship had been going for some time. Miss Cox is expecting her baby in November. Can you imagine Liberal Democrats in the old days letting a Tory candidate in the same situation go through the entire campaign without alerting the electorate to this interesting situation? Plainly, the Conservatives and Labour aren't in the same league as the Lib Dems when it comes to blackening their opponents in a discreet sort of way, but it is disappointing that the other parties failed to give the electorate the opportunity of reflecting on their candidate's moral credentials.

However, Mr Hemming has undoubtedly done the right thing having done the wrong thing - by not crowning his adultery by deserting his wife and children. His wife has risen to the occasion magnificently. In a declaration of what can only be described as family values, she declared: "So many problems in society are caused by single parents and the breakdown of the family and while John is obviously very concerned with improving people's lives, he has only added to the problem."

Brilliant. That's telling them. And if the Hemmings were Tories, Mrs Hemming would be a party heroine, with a strong claim to a safe seat all of her own. But this willingness to identify adultery and single parenthood as the social evils that they are - isn't it a bit difficult to square with the Lib Dems' notorious moral latitude? This, after all, is the party of gay marriage and contraceptives for the young. The trenchant moral line that Mrs Hemming has laid down may not play with her constituency party - especially since Miss Cox is also a Lib Dem councillor.

But perhaps, tucked away beneath the party's dogmatic non-judgmentalism on sexual matters, there is scope for the kind of sentiments that Mrs Hemming has articulated. When Charles Kennedy gave a lecture to the Faithworks organisation, he praised the inspiration he got from his own parents' solid union. He wouldn't have said that sort of thing to an audience of Lib Dems, but it just goes to show that there may be an unobtrusive home for family values somewhere in the party.

While the Lib Dems produce this unexpected instance of marital solidarity, the Tories seem to be losing their tradition, not of adultery, but of penitent adulterers. The distinction of producing the first post-election sex scandal fell to the Croydon Tories, whose MP, Andrew Pelling, left his wife of 18 years for a constituency worker nearly half his age called Lucy. So far as I know, since the revelation there hasn't been a peep from Mr Pelling's constituency association.

Mrs Hemming also deserves applause for her frank declaration that she feels "betrayed and hurt". The one thing that never rings true when a spouse commits adultery is the line that the situation remains amicable. Liars, liars, liars. Adultery hurts, and Mrs Hemming is right to say so. A pity, then, that Mr Hemming declined to confirm that his affair with Miss Cox was now over. Mrs Hemming should get it in writing.