Marriage came at a price for Alan Miller — £4,935.83 a day, to be precise. The 2¾ years the 41-year-old fund manager shared with his American-born wife, Melissa, did not produce any children, but she gave up her £85,000 job anyway, to divide her time between their newly refurbished Chelsea town house and the villa in the south of France. So when the Court of Appeal ruled this July that Melissa Miller, 36, should leave the short, ill-fated marriage with £5m of her husband's wealth, a flurry of consternation swept through London's legal establishment. Why, demanded eminent QCs and £350-an-hour family lawyers, were the judges once again hammering a rich husband simply to fund an ex-wife's lavish lifestyle? What attraction would matrimony ever hold to high-earning men if even a brief, childless union could imperil assets accumulated well before they tied the knot?

The prospect of divorce has in recent years begun to terrify rich British men. In a series of landmark cases since 2000, the divorce courts in England and Wales have given nonearning divorcées expectations of ever-greater stakes in their husbands' fortunes. Not even American-style prenuptial agreements can protect them: despite the growing popularity of "prenups" over here, the courts are not obliged to enforce them.

For centuries, the divorce courts have favoured the man in his role as traditional breadwinner, awarding him the bulk of the marital fortune once the wife's "reasonable requirements" for day-to-day living have been met. It took a ground-breaking House of Lords judgment five years ago to challenge this historic bias. The case did not, as you might expect, involve celebrities slugging it out over the rights to ownership of yachts or villas. Instead, it focused on an extraordinarily low-profile couple who had built up a dairy farm.

As a result of this judgment, equality would be the new yardstick in divorce settlements. The nonworking homemaker and child-rearer would have as much right to the family wealth as her husband. Since then, senior judges have issued increasingly wife-friendly rulings, forcing husbands to cede ever-larger stakes in their future income, and encouraging wives' lawyers to target even the man's inheritance. Independently wealthy women, too, face greater uncertainty about what happens to their money after divorce. But almost all the significant cases to have reached court so far have focused on just how much the husband will have to hand over.

These high-profile judgments are redefining divorce law in England and Wales, establishing constantly shifting rules for the thousands of "big money" break-ups that settle quietly out of court. (The law differs in Scotland and Northern Ireland.) The lawyers, meanwhile, are constantly seeking to test the boundaries to optimise their clients' financial position. As a result, large numbers of cases are being thrashed out in court.

Now some of our most senior family lawyers are speaking out. The new judicial mood, they suggest, threatens to weaken the institution of marriage itself. If ambitious, high-earning men see the legal odds stacked against them as never before, why, the lawyers ask, will they ever risk marrying in the first place?

As Alan Miller sees it, he has been the victim of legally sanctioned burglary. "It's as if someone's come into your nice home, taken away a lot of its contents, and then the police have come round and said, 'We've found the thief, but sorry, you're rich, so there's nothing we can do.' This is so ridiculously unfair and discriminatory."

Not that Miller cannot afford a £5m payout: as manager of a large City hedge fund, he earns up to £3m a year, owns a £6m house in Chelsea, and in March 2000 received £20m following the earlier sale of Jupiter, a previous employer, to Commerzbank. Then there were the 200,000 shares he received on joining his current employer the following January, potentially worth a further £20m. But these windfalls, he says, were negotiated well before the wedding in July 2000, and owed nothing to Melissa's contribution as his wife. Only a "gross injustice", he adds, could explain how she could leave the marriage after just 1,013 days with his former £2.3m Chelsea house and a £2.7m lump sum. That, the court calculated, would give her a lifelong annual income of £98,000 tax free, enough to "live to a very tolerable standard".

"It's ridiculous that a third of my assets at the time of the marital breakdown, which were all earned prior to the marriage, should be given to my wife," Miller protests at the Park Lane office of his solicitor, Raymond Tooth, in his only interview since the Court of Appeal ruling. Tooth is seeking to challenge this ruling in the Lords.

Lord Justice Thorpe, in the appeal court, recognised that Miller's wealth had afforded his wife an unusual degree of luxury: previously, Melissa had lived in a one-bedroom rented flat while working for a pharmaceutical company in Cambridge. But through marriage she gained "a legitimate entitlement to a long-term future on a higher plane of affluence", the judge ruled.

"Yes, we went on expensive holidays, and she enjoyed buying expensive clothes or shopping for antiques in the south of France," her former husband recalls. "I never realised that if it didn't work out there would be a financial penalty for my being generous.

"She worked for half of the marriage and had a relaxing time for the other half, spending much of her time shopping for the house I bought in France." He shakes his head, and sighs in cynical exasperation. "You know, her e-mail address starts off with 'Must-do-lunch-Melissa'. And she's never bothered changing it."

This is, of course, just one interested party's account. Melissa, approached through her solicitor, did not respond for this article, but the judge in the initial court hearing, Mr Justice Singer, was in no doubt that her husband was at fault. Miller's "irritation" with his wife's personality and behaviour had, the judge said, reflected "more his lack of adaptability than any shortcomings on her part". By pursuing an adulterous relationship, with a woman whom he has since married, Miller was found "largely if not entirely" responsible for the marital breakdown, a factor that boosted his wife's award. This in particular raised concern in legal circles. It seemed to revive the long-abandoned notion that "blame" should be taken into account when determining a financial settlement.