The Big Question: Has divorce become too expensive for the rich?

How much does Heather Mills McCartney stand to win in a divorce settlement?

Anything from £30m to £200m. In America, Australia and many European countries, only the assets amassed by the couple during the marriage are considered in financial settlements - a policy known as "marital acquest". But British case law is based on the idea that all the wealth brought to the marriage by both parties is potentially up for grabs. However, predictions that she could be awarded half of her husband's £830m fortune are thought wide of the mark, partly because the marriage only lasted four years. In Lady McCartney's favour is the fact they have a child together. Patricia Hollings, a barrister at the law firm Finers Stephens Innocent, said: "I think it will come down to something between £50m and £100m."

Should Sir Paul have signed a pre-nup?

Yes. While pre-nuptial agreements are not technically valid under British law, the courts do taken them into account when deciding on a financial settlement. If a pre-nup had been signed, with proper negotiation and legal representation of both husband and wife, and is considered to be generally fair, it will have a major bearing on the ruling. In a landmark 2003 case known as K v. K, a wife had signed an agreement that gave her £120,000 in the event of a split. When she and her husband did divorce, however, she demanded £1.2m. The courts stuck by the pre-nup.

How are the super-rich cases decided?

The case that the legal world - and now probably the McCartneys - is agog to see settled is Miller v. Miller. The House of Lords is due to rule on Wednesday whether Melissa Miller should be allowed to keep a £5m settlement awarded to her following the break-up of her two-year-and-nine month marriage to her husband Alan.

The case is similar to the McCartneys in that the marriage was short and the wealth all rested with Mr Miller, a fund manager worth £30m. The original judge ruled that the former Mrs Miller was entitled to a substantial slice of her husband's fortune because she had entered into the marriage with a "reasonable expectation" of a future wealthy lifestyle.

The word among divorce lawyers is the Lords will uphold part of that ruling, but that they are "troubled" over whether the settlement should be based on all the assets owned by Mr Miller or simply those acquired during the marriage. That point could be crucial for many other cases where a person marries someone much wealthier than them.

Have settlements got more expensive over the years?

Yes. After centuries during which the wives of the rich (and not so rich) had no claim on their husbands' assets and even lost custody of their children if they divorced, the last five years have seen profound changes. The 1969 Divorce Reform Act made it easier for couples to split and the 1973 Matrimonial Causes Act made it clear that the future financial needs of spouses should be taken into account, but it was the 2001 case of White v. White which is seen as the turning point in British divorce law. That case established the principle that the contributions of a "homemaker" spouse were equally valid to the building up of assets by the "breadwinner' partner.

The divorce settlement between the footballer Ray Parlour and his wife Karen saw another shifting of the pendulum when a judge ruled that she was entitled to a third of his future earnings because of her role in building up his success. Adultery is also now an aggravating factor in financial settlements. The judge in the Miller case said she was entitled to more because she was "committed" to the marriage, while her husband had committed adultery.

Can the rich do anything to protect their assets?

Britain is now considered to be one of the most expensive places in the world to divorce, so jet-setters could try having their cases heard in a more millionaire-friendly country. Even the lack of a marriage cert is no guarantee of hanging on to your millions. Mick Jagger tried to claim that his Bali marriage to model Jerry Hall was not legally valid, but that cut little ice against the fact they had four children together, and she was awarded £30m.

Sir Paul, however, has one factor in his favour - his musical talent. If a spouse can prove their wealth was generated by a "spark of genius" from them alone, they may be able to hold on to more of the money.

This so-called "stellar contribution" principle has it roots in the rather unglamorous world of bin bags. Michael Cowan successfully argued in his 2001 divorce that his wife Jacqueline had played no part in the amassing of his £12m fortune from the manufacture of black bin liners, and he was therefore entitled to a larger slice of the money.

The "spark of genius" argument has only worked in a handful of cases since, although Sir Paul should be able to convince even the most out-of-touch judge that as one of the songwriters behind arguably the world's greatest band, he does have some right to such a claim.

So who wins in the world of celebrity marriage break-ups?

If Lady McCartney wins a similar settlement to Melissa Miller, she will receive around £1m for every week she was married - an eye-watering amount compared to the £165,000 in total assets that the average divorcing couple in Britain end up dividing. But her estranged husband earned a reported £48m last year alone from album sales and his American tour. He will go on earning millions from royalties, while his estranged wife,may find her future earnings more limited.

Ultimately, however, it is the lawyers who win. In White v. White, the couple whose divorce sparked a new era of multi-million settlements, more than £800,000 of their £4m fortune went on legal fees. Mrs White is still involved in protracted litigation and says that the ruling, in the end, did nothing for her.

Is divorce expensive for the rich?

Yes...

* Britain has among the most generous divorce laws in the world for the less wealthy spouse

* Case law is based on a divorce in which a woman won £5m for a marriage to a man worth £30m and which lasted less than three years

* Pre-nuptial agreements are not valid under English law, meaning the rich can be taken for everything they own

No...

* Many lawyers believe that after decades of divorce discrimination against women who give up work to support high-earning husbands, the pendulum is now swinging to a more balanced position

* The super-wealthy tend to have investments - or royalty earnings - that enable them to recoup the money they pay out

* The law still allows a spouse who has made an exceptional financial contribution to the marriage to keep the lion's share