Luisa Dillner: Mothers-in-law are lovely, in their place. Their own place, that is

The round-the-clock adviser may be the butt of many jokes, and didn't go down a storm chez Cole, but most families rub along

It's not Ashley's fault. The person who ruined the Coles' marriage has been identified (allegedly by friends of Ashley) as that archetypal pantomime villain – the mother-in-law. More potently, in this case it's a Geordie mother-in-law, the diminutive Joan Callaghan, who was drafted in to live with the couple in their Surrey mansion after Ashley's first marital transgression. Known as the "pocket rocket", Joan was said to have adopted the role of looking after Ashley and the couple's two dogs. Joan had already brought up five children on a Newcastle housing estate so this should have been a breeze. But apparently Ashley told friends that since she arrived he and Cheryl "haven't had room to breathe", that his mother-in-law "took her daughter's side in everything" (like the rest of the country, then) and that they couldn't even have a row.

The most cutting accusation is that Joan ruined their sex life. Instead of rushing to the marital bed, Cheryl apparently preferred to stay up watching the television with her mother. What's a football star to do but to allegedly play computer games for hours and send sexy texts of himself to various women. "It's a bit of a passion-killer having your mother-in-law in the house," he is reported to have said.

Usually, you could blame a mother-in-law for just about anything and generate widespread support. No one stands up for mothers-in-law. It is a measure of the low esteem in which the public hold Ashley's infidelities that no one's buying it.

Despite unflattering newspaper pictures of Joan looking like the stereotypical battle axe of a mother-in-law, seeping disapproval of her son-in-law, the country is firmly on her side. If she did indeed pour vitriol down the phone at Ashley, he clearly deserved it. For once, the mother-in-law is the voice of reason, the barometer of the feelings of ordinary folk. Single handedly, the straight-talking Joan Callaghan may finally be giving mothers-in-law a good name.

They could certainly do with it. Historically mothers-in-law have been the butt of jokes and the subject of more serious vilification. It's a role that has existed throughout the ages but not one that women have actively chosen or usually enjoyed. Mothers-in-law are traditionally accused of being interfering, overbearing, of visiting their family too often, staying too long and refusing to accept that anyone could be good enough to marry their son or daughter.

The loathing of mothers-in-law is a global phenomenon. The Scottish anthropologist Sir James George Frazer remarked, "The awe and dread with which the untutored savage contemplates his mother-in-law are amongst the most familiar facts of anthropology."

Margaret Mead, also an anthropologist, put the boot in when she said, "Of all the people I have studied, from city dwellers to cliff dwellers, I always find that at least 50 per cent would prefer to have at least one jungle between themselves and their mothers-in-law." In Ashley's case the nine bedrooms of their roomy mansion didn't afford quite enough distance between him and his mother-in-law.

If there is any doubt about the longstanding low status of mothers-in-law, there is evidence of their being treated harshly since Roman times. The first-century satirist Juvenal warned that they taught their daughters "evil habits", and said couples should "give up all hope of peace as long as your mother-in-law is still alive".

Juvenal's satire is considerably more subtle than modern quips about mothers-in-law. Jokes about them took off properly in the Victorian music halls, where songs and gags came from men's personal experiences: housing shortages meant men often lived near or with their mothers-in-law. Comedians told jokes about being ganged up on by powerful women – the mother-in-law was usually laughed at for being ugly, overbearing and mean. These jokes exist in many languages and whatever the nationality of the mother-in-law, the formula these jokes follow is the same.

How truly misogynistic these jokes are is debatable, although they disappeared overnight in the wave of political correctness brought in by alternative comedians. Les Dawson, a comedian famous for his mother-in-law gags, is said by Tracy, his widow to have adored his mother-in-law. She maintains his jokes were affectionate and told with a twinkle in his eye.

With gags such as "My mother-in-law said, "One day I will dance on your grave." I said, "I hope you do. I will be buried at sea." And, "I took my mother-in-law to Madame Tussaud's Chamber of Horrors and one of the attendants said: 'Keep her moving sir, we're stock-taking.'" It's hard to see how he could have caused any serious offence. A study of mothers-in-law by Pamela Cotterill, a lecturer in sociology and women's studies, found that they tended not to be upset by jokes because they seemed so far fetched they couldn't apply to them, but they didn't find them funny. Cotterill also found that daughters-in-law didn't find them funny either, largely because they could see that one day they'd be applied to them.

Men may tell jokes about them, but they usually have better relationships with their mothers-in-law than women do with theirs. The real conflict occurs in relationships with their daughters-in-law. This is where things get personal and emotions are heightened. Dr Terri Apter, a psychologist at Cambridge University recently studied 49 couples and found that two-thirds of the wives in her sample said their mother-in-laws caused them "long-term unhappiness and stress", compared with 15 per cent of the husbands. This agrees with an earlier, large survey in America in the 1950s by Dr Evelyn Millis Duvall, a mother-in-law herself, who also found that the most difficult in-law relationship was that between mothers-in-law and daughters-in-law.

Mothers-in-law were accused of being possessive of their sons and critical of their daughters-in-law, especially over childcare and house work. The same survey, however, found very little criticism by mothers-in-law of their daughters-in-law. Most mothers-in-law expressed bewilderment as to what they had done to irritate their son's wives and partners. Not all mothers-in-law, however, are blameless. Websites such as "Disarming the Dragon" and "The Secret Society of Tortured Daughters-in-law" list gifts from mothers-in-law to their daughters-in-law, such as used deodourant, toilet rolls and birth control pills, that clearly give mothers-in-law a bad name.

The relationship between mothers-in-law and daughters-in-law is inherently problematic because women don't want to be shunted from being the mother at the heart of the family to the unpopular role of mother-in-law. It's hard for mothers-in-law who have already brought up a family and feel they have so much knowledge to impart, to keep quiet. Yet any suggestions are often viewed as criticisms by daughters-in-law who want to find their own ways of doing things and increasingly feel stressed at combining working with family life. Add the facts that both women care for the same man but in different ways and that the mother-in-law is grappling with the menopause as the daughter-in-law is thinking of conceiving, and it's an emotionally loaded relationship.

But mothers-in-law have an enormous amount to offer. First and foremost, yes, they do stick up for their sons or daughters, a function that is sometimes sorely needed. Throughout history, they have done their formidable best to protect their daughters from men who they felt did not have their best interests at heart.

Mary Moffat trekked alone across great swathes of Africa to make sure Livingstone was looking after her daughter properly. Livingstone, who was fairly careless of his wife and children's well-being, was shamed by his mother-in-law into building a proper shelter with a roof for them, although he kept taking his pregnant wife on dangerous excursions, one of which killed her.

Mme de Montreuil got so fed up of de Sade cheating on her daughter with a succession of prostitutes (some of which he tortured horribly), as well as seducing her younger daughter, that she got him arrested and locked up for over a decade.

As well as their avenging role, mothers-in-law can provide practical support. Barack Obama credits his mother-in-law with enabling him to reach the White House, by supporting the family's domestic arrangements. Marian Robinson was drafted in somewhat reluctantly from her life in Chicago to look after her granddaughters. She is careful not to join the Obamas for every evening meal and family holiday, and has a bedroom on a different floor from her daughter and son-in-law. She clearly follows best practice for mother-in-laws by not interfering and keeping some distance.

Perhaps the White House is that much bigger than the Coles mansion. Whatever the reason for the Coleses' estrangement, Cheryl said some time ago that the only people she trusted were her mother and the dogs. Mother may go too, if Cheryl's career takes her to America. Joan may be the poster babe for mothers-in-law, but the best of the breed should avoid getting too involved in their offspring's relationships. Mothers-in-law who have their own independent lives and help out when needed, have the most to offer.

Luisa Dillner is the author of 'The Complete Book of Mothers-in-Law'