Paul McCartney and Heather Mills have failed to reach agreement in what could be the biggest divorce payout in British history.

Judgment has been reserved in the divorce hearing, and the size of the settlement will be decided in the next few weeks.

A High Court judge will work out how much the former model will pocket from the musician's estimated $1.6 billion fortune.

The couple have spent a week and a day in court behind closed doors.

Nicholas Mostyn, who has been representing the former Beatle, confirmed as he left court that the judge had reserved his ruling.

This means rumors the couple had reached a settlement over the weekend were unfounded.

McCartney was not in court Monday for the hearing. But TV pictures showed a smiling Mills leaving the courtroom with her entourage.

She made no comment as she left. She was then driven off in a black Mercedes.

Mostyn had put Sir Paul's side of the argument and today it was Mills' turn to reply to any points he made before the judge reserved his ruling.

The judgment will be binding on the pair, but could be challenged at the Court of Appeal if one side is unhappy.

But that would entail a dramatic change — no longer would the accusations from both sides be kept secret behind closed doors.

Sir Paul is anxious to keep the details of his four-year marriage to Mills, who lost part of her leg in a road accident, out of the public domain.

But she has no such qualms — and is reported to be planning a book on the subject which has the potential to earn her millions worldwide.

They married in June 2002, four years after Sir Paul's first wife Linda died of breast cancer.

There has been speculation that this could be the most expensive divorce in British legal history with Sir Paul, 65, forced to pay in the $100 million range.

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But this now seems increasingly unlikely with the judge able to take into account factors including the short duration of the marriage.