The Christmas party season is almost upon us, bringing with it all the usual anxieties: what to wear, how to avoid the office bore, how to find a taxi home. And, for anyone wondering about the activities of an absent spouse, 'Is my partner cheating on me?'

It may not be the most obvious question for busy people caught in negotiations about whose family to visit and whether to have turkey again. But we are now about to enter a paranoid world, in which husbands and wives are racked by anxiety. And that anxiety is about to be reinforced by the opportunity to buy a simple kit that will tell them whether or not their partner is committing adultery.

Described cheerfully in the promotional literature as the Five-Minute Infidelity Test Kit, it encourages suspicious spouses to behave like private detectives. You don't need scientific training, just simple instructions on how to do the test and 'put an end to the nightmare of suspicion and deceit caused by the infidelity of a cheating spouse!'

All you have to do -- brace yourselves -- is test your partner's underwear for traces of semen (a positive reaction will show up purple on a piece of blotting paper, leaving no tell-tale stain on the garment itself). It also works on his car upholstery, or her unwashed sheets, although the use of a condom will make a positive result more difficult to obtain.

Sufficient material to carry out the test five or six times costs £59.99. The kit comes in 'discreet' packaging and will show up on your credit card or bank statement under an anodyne heading, in case your partner is doing some checking of his or her own. The 'evidence' thus obtained has not yet been tested in British courts but the makers report that divorce lawyers become 'confident and even aggressive' when shown a positive result.

If testing your partner's pants seems a trifle sneaky, the kit's makers also suggest that it's easier and cheaper than spy cameras, lie-detector tests and private investigations. Yet nowhere in the promotional literature is there any recognition that a marriage or relationship that has reached this point -- the domestic equivalent of the cold war -- is in deep trouble.

Other statistics, such as the fact that one in 15 users lives in Brighton, appear almost random. The makers assure potential customers that the test will work even on stains that are two years old, as long as the garment has not been washed, which suggests that some of them may have even more pressing problems with their spouse's personal hygiene.

But the most disturbing thing about the kit is the confusion about what it is offering. The underlying suggestion in the extremely bullish literature -- 'Be creative in your search!' -- is that using it will make you feel better. If you do the test on your wife's clothes and get a positive result, then she's 'busted'. It doesn't add that she might be very angry, even if it's negative. Who wants to live with a spy?

People's attitudes to sexual fidelity vary widely. For some, it is very important. For others, this kind of sleuthing is far worse to contemplate than sleeping with someone else. Even the statistics quoted by the makers of the kit -- 60% of men and 40% of women have an affair during marriage, they claim -- show that lifelong monogamy is an unrealistic goal.

It is not difficult to imagine a situation in which using the test might lead to domestic violence. Or to the acrimonious end of a relationship in which young children are involved. The only mentions of children in the promotional literature, by the way, is a warning that they shouldn't swallow the contents of the kit, and the suggestion that parents might like to use it to check up on their kids, which is hardly a recipe for family harmony.

'CheckMate is the only product of its kind that can actually monitor your spouse's sexual activity outside the relationship,' the makers' website www.getcheckmate.com announces. If this is true, it is a testament to the fact that advances in technology do not always represent progress for humankind. It may be a technical innovation, but the idea behind this ghastly device is as retrograde as the chastity belt.