When David Lloyd George was caught cheating on his wife, he wrote to her saying it was her fault for being in Wales looking after the children, leaving him alone in London. God will judge you, he said.

When David Lloyd George was caught cheating on his wife, he wrote to her saying it was her fault for being in Wales looking after the children, leaving him alone in London. God will judge you, he said.

His effrontery raised a laugh at the Edinburgh International Book Festival when Ffion Hague read the excerpt from her book on the women in his life. The long-suffering Mrs Lloyd George never left him in spite of his repeated infidelities; nor did his mistress, Frances Stevenson, who had two abortions to spare him professional embarrassment. She married him after he was widowed.

Someone told me recently about a man who had met both Lloyd George and Churchill. He said that when you met Churchill, you knew he was the most important person in the world. When you met Lloyd George, you felt that you were the most important person in the world.

That is the skill of the womaniser. They are a type - charming, often amusing, attentive, empathetic and relentlessly unfaithful. It doesn't matter whether they live in a palace or a pigsty; whether their wife is a beauty or a blight on the eye, a saint or a scold. Irrespective of whom they marry or how often they marry, sooner or later they will be back on the prowl in search of a new sexual partner. James Goldsmith was another of the breed.

Paul Newman, by contrast, when asked in an interview why he was faithful to Joanne Woodward, his wife of many years, famously quipped: "Why go out for hamburger when you have steak at home?" I have always thought the smartest thing a woman can do is to marry a man with Newman's nature and attitude. There are no guarantees in life. He might have an affair, but it lowers the probability.

Statistics suggest that half of all men are unfaithful. The question is: whose fault is that? According to a new book that is causing a stir in America, the answer is their wives.

The book is called The Truth About Cheating: Why Men Stray and What You Can Do to Prevent It, and it matters because it is written by an influential man who is taken seriously by opinion-formers.

M Gary Neuman is a well-known marriage counsellor and rabbi who appears on primetime American television and writes in serious journals. He will be discussing the book on Oprah next week.

Neuman noticed that research into infidelity centred on how wives cope with it and decided to focus on their straying husbands. He questioned almost 100 unfaithful men (and a similar number of faithful men) across the United States. His research has thrown up some interesting material. For example, men say that emotional dissatisfaction within marriage is a much bigger factor than sexual dissatisfaction.

What is unfortunate are the conclusions Neuman has drawn. Faced with new insight into why men betray their wives, he has drawn up a list of "what wives can do to create a solid marriage". He is quoted as saying: "If a husband has cheated, his wife's role is to recognise that she needs to change."

Reading his recommendations, it's hard to know whether to laugh or cry. To keep their husbands faithful, wives should be slim, even-tempered, sexually available and emotionally attentive. A wife should take care to heap praise on her husband's ability to provide for the family (even if she earns more than him). She should discourage nights out with the boys and instead she should share in his hobbies. In other words, she should never let him out of her sight.

Forget any idea of marriage being an equal partnership with a like-minded soul who hopefully shares a sense of humour and with whom you can be spontaneous and have fun. Forget about trust. Believe what you read and you must conclude that a good wife is a cross between a geisha and a gatekeeper.

I suppose it might work for a man who fancies being super-glued to Pollyanna from here to eternity. But most real husbands would soon start inventing regular business trips just to get room to breathe.

I don't intend to make light of the real distress that infidelity causes. The book charts organisations that will provide false invitations to weekend conferences for cheating men to cover their tracks. It interviews men who for years invented regular work in out-of-town offices to disguise visits to their mistress. It states that 69% of men won't admit to adultery until they are confronted with hard evidence. Women who are dealing with the pain and insecurity that is the consequence of betrayal will naturally seek solutions. But this book is a dangerous blind alley.

Husbands (and wives) who are not serially unfaithful have an affair for a thousand reasons. They meet someone attractive who is attracted to them. They are flattered. They feel rejuvenated. They get carried away by the wonder of it all. When you boil it down, people are unfaithful because the draw of the new experience is greater than the loyalty to the known. It may coincide with a dull or difficult patch in their marriage but it isn't a simple matter of cause and effect.

When Neuman questioned men who had been unfaithful, he asked them if they were experiencing dissatisfaction with their marriage. Eighty per cent said they were. Remember Lloyd George. It's always easiest to put the blame elsewhere. What would the survey have revealed if he'd asked: were you feeling selfish? Did your ego need a boost because of problems at work? Have you achieved less than you'd hoped? Do your friends earn more than you? Was this the only woman (apart from your wife) who was overtly keen on you?

The danger with books like this is that while they pretend to do good, they do the opposite. Betrayed wives may blame themselves for their husband's affair. Disloyal husbands will have an excuse to blame their wives.

The one bright note is that Neuman reports he didn't meet a single husband who was cavalier about his actions. Not one of them wanted to have another affair and each wished he could retract.

Even those who felt their wife's behaviour was a strong factor in their infidelity felt remorse.

There is, of course, a grain of truth in the book. It is common sense that a man who is not an inveterate womaniser, and who meets someone both attractive and available, will be less likely to embark on an affair if he enjoys a comfortable and happy home life than if he lives in an uncomfortable war zone. It is a statement of the blindingly obvious.

The best advice I heard handed out at a wedding came from the father of the groom. He said to the couple: "Be good to each other."

It's as much as anyone can be. Neuman has just trotted out the worn, tired old formula of the Stepford wife. But, in the lurch-along journey in a three-wheeled van that is marriage, the only man she will really suit is a Stepford husband. And who would give him house space?