She did it for Macca — now she can do it for Madonna. Fiona Shackleton, the divorce lawyer who ensured that Sir Paul McCartney retained all but £24.3 million of his £825 million fortune, has been lined up by the 49-year-old pop star.

Madonna, whose fortune is estimated at £300 million, is understood to be seeking legal advice on a possible divorce from her husband of seven years, the film director Guy Ritchie.

Ms Shackleton, 52, is the lawyer of choice for the rich and famous after what was regarded as the spectacularly well-handled split of Sir Paul from Heather Mills, who was pushing at one point for as much as £80 million.

Dubbed the “steel magnolia” for her tough but pragmatic negotiation tactics, Ms Shackleton instructed the top divorce silk, Nicholas Mostyn, QC. This so-called legal dream team secured such a successful result that Ms Mills, in fury and frustration, emptied a jug of water over Ms Shackleton’s head after hearing the judge’s ruling.

Madonna’s spokesman refused to comment today on claims that the singer has instructed the lawyer who came to prominence when she acted for the Prince of Wales in his divorce with the late Diana, Princess of Wales.

Ms Shackleton, of the London law firm Payne Hicks Beach, once said: “I like sticking up for people. It helps to have a rod of steel through your back and lots of charm, People generally choose the lawyers they deserve.”

The word in legal circles today was that the Madonna and Guy Ritchie had previously used another leading City law firm, Withers, on either a tax or property matter. Although Withers has a similarly high reputation for “big money” matrimonial cases, it was unable to act for Madonna in any potential separation because of its previous involvement with the couple.

The case was passed to Ms Shackleton. Withers declined to comment today.

Ritchie is thought to have had dealings with a lesser-known Mayfair law firm, Forsters, but which nonetheless has a good reputation in matrimonial law.

Today Ann Northover, partner in the divorce and family partner, would not confirm or deny the firm’s involvement with Mr Ritchie. She said: “I can only say I have no involvement at the moment.”

Forsters has more than 100 lawyers and is best known for its leading commercial and residential property practice.

There has been speculation for some time over the marriage of Madonna, 49, and Ritchie, 39, and it is believed that the pop star met Ms Shackleton in April for a preliminary meeting.

It is thought that the couple did not have a pre-nuptial agreement, which means that the starting point for any settlement would be a split of 50-50. Avariety of factors such as the length of the marriage and the wealth brought to the marriage by Madonna, in particular, would then be taken into account.

James Stewart, a family partner with the leading London firm Manches, said: “These big money divorces are either terribly straightforward, because there is enough money to give those involved a fair share — more so than where there is not much money —or they go to court, because one side is either mean or greedy.”

Ann Northover, of Forsters, said: “There is still great uncertainty in these very big money cases as to how they are to be decided. We have had very helpful guidance in the case of Charman [the biggest divorce award made by the courts in legal history] which reaffirmed equality in the division of assets.

“But this is subject to departure, depending on factors such as the length of a marriage, how the matrimonial assets were created; the special or stellar contribution that either one of the couple, such as Madonna, may have made before the marriage.”

Without a pre-nuptial agreement, Ritchie could be looking at as much as £50 million of Madonna’s £300 million fortune. Lately the star has been seen out without her wedding ring, fuelling talk of a rift.

Madonna and the concert promoter Live Nation Inc have announced a deal that will give the company an all-encompassing stake in the music of the Material Girl, the latest big-name artist to break ranks with a leading record label. Financial terms were not disclosed in the joint statement released by Madonna and Live Nation. The deal is worth about $120 million (£60 million) over ten years

Big sales around the world for Madonna's upcoming Sticky & Sweet tour have been overshadowed in music industry circles by chatter about the large number of tickets still available for a key stop in Los Angeles in November and softer-than-expected sales of her latest album Hard Candy.

The tour so far has grossed more than $74 million in sales for 13 dates in Europe and piled up a string of sellouts at arenas across North America, according to Live Nation.

Arthur Fogel, chairman of global music and CEO of the global touring division at Live Nation, projects that the tour will gross more than $250 million in ticket sales — surpassing her record-breaking Confessions on a Dance Floor tour two years ago, which pulled in $195 million worldwide.

If any divorce between Madonna and Ritchie goes to court, it could provide another chance for guidelines in “big money” cases which lawyers say are needed. The Law Commission said recently that it would not be reviewing the law on the division of assets on divorce — much to the dismay of lawyers.

Mark Harper, a partner at Withers, said that the omission had caused “dismay amongst the family judges and lawyers”.

“The Court of Appeal in Charman called for fundamental review and reform of the law which the Government has ignored to save money; all that will happen is that the wealthy will continue to litigate the uncertainties of the case law which will continue to clog the courts. “

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