Divorce lawyers who have watched with gruesome fascination the escalating hostilities between Paul McCartney and his estranged wife Heather Mills believe the couple are sleepwalking into a minefield that could spring some nasty surprises. “This is madness,” says one.

The split between the 64-year-old former Beatle and his 38-year-old wife was emphasised last week when Mills hired the solicitor who represented Diana, Princess of Wales at her divorce, in perfect symmetry to McCartney’s chosen lawyer, who acted for Prince Charles.

Anthony Julius of the firm Mishcon de Reya won Diana a £17m settlement, leading Geoffrey Bignell, Charles’s financial adviser, to claim: “She took every penny he had. She took him to the cleaners.”

The prospect of a Charles vs Diana rerun is slightly misleading, however. McCartney is much richer than a mere prince, and under present rules he stands to lose only a fraction of his wealth. He appears to have stolen a march on his wife by quickly lodging a petition in Britain, effectively pre-empting a divorce in America, where wives are routinely awarded half the communal property.

Mills is reported to have set her sights on a settlement of £200m, nearly a quarter of her husband’s £825m fortune as calculated by The Sunday Times Rich List. If so, she could be sorely disappointed. “There’s absolutely no way she’s going to get £200m,” says Vanessa Lloyd Platt, a leading family lawyer. “I think we’re talking £25m- £50m tops.” Mills could end up with less than the £30m she is said to have turned down.

However, “friends” of Mills said last week she would “come out fighting” after the humiliation of being barred from McCartney’s London home and finding the locks had been changed. To add to tabloid entertainment, police were called when her security guard tried to climb a fence. McCartney had earlier frozen their joint bank account, it was reported.

The minefield they are both approaching is the divorce court — something most rich couples are now going to great lengths to avoid. Recent precedents in matrimonial law have made the outcome a lottery. “Neither the solicitors nor the judges have a clue,” says Lloyd Platt. “If you put 10 lawyers in a room they will all give you a different conclusion on what they think will happen.”

In such a volatile climate, McCartney also faces the risk of a painful setback if the case goes before a judge. Yet an out-of-court settlement looks increasingly remote, Lloyd Platt believes. “In view of what has been played out in the press over the last few days, it looks as if it might be turning into a battle of all battles. It’s escalating out of control.”

Mills may campaign against landmines, but her husband is better protected against the legal fall-out of divorce. The explanation lies in the basic equation for calculating who gets what, hammered out in recent case law.

The starting point for long marriages is a 50-50 split of a couple’s assets. But with a short, four-year marriage such as the McCartneys, the amount to be carved up is limited to the assets made during their marriage. In other words, McCartney’s pre-marriage assets, which constitute the bulk of his wealth, are ring-fenced. So Mills could be looking at 50% of their post-marriage wealth.

Paradoxically, Mills’s cut could be shaved down further in the light of the recent case of John Charman, the insurance magnate who was ordered to pay his wife £48m in what is believed to be the largest divorce award made by a British court. In fact, Beverley Charman received only 37% of the couple’s £130m fortune instead of the 45% she was seeking because her husband’s “extraordinary talent and energy” had contributed so much to their wealth.

The Charmans had been married for nearly 30 years, so different rules apply, but it is the “genius factor” that McCartney can invoke to his advantage. According to Lloyd Platt: “He could argue that a lot of the after-marriage assets were off the back of already acquired assets, such as the royalties on already written music. So there could be an argument for saying that some of those should be ring-fenced as well.” But the Charman ruling is going to the Court of Appeal, so the ground could shift again.

Mills holds two strong cards. The first is the couple’s two-year-old daughter Beatrice. “The court won’t allow her to be put up in a small suburban semi if the child will be spending time with Paul McCartney in the lap of luxury,” says family lawyer Philip Rutter.