A London trader won a court ruling to cut her husband's divorce settlement after judges said their "short, childless" marriage warranted a diversion from the UK's tradition of enforcing an equal split of assets.

Julie Sharp, an energy trader who earned £10.5 million ($17.8 million) in bonuses during their six-year marriage, won a London appeals court ruling on Tuesday cutting the payout to her ex-husband, Robin Sharp, to £2 million from £2.74 million ($4.64 million) awarded in 2015.

The couple, each in their "early forties" with no children, married in 2009 before Julie Sharp filed a divorce petition in 2013.

The ruling is the latest retreat from London courts' traditional policy of splitting assets equally during divorce cases. In other cases over the past two years involving bankers and wealthy couples, judges have used a theory known as "special contribution" to cut non-working spouses' share of the marital possessions.

"This groundbreaking ruling ultimately dictates that marriage is no longer a financial partnership in some circumstances," said Alex Carruthers, a family lawyer at Hughes Fowler Carruthers. "This raises far more questions than it answers."

Aston Martins

Although Robin Sharp was aware his wife made a lot of money, he was never privy to the details, and she funded the couple's holidays and bought him three Aston Martin cars, the court said.

In 2013, difficulties that would soon lead to the divorce had become apparent. Robin Sharp started a "clandestine affair" in February of that year and its full extent only surfaced while he was testifying in May 2015, according to the judgment.

"The husband made no contribution to the source of the wife's bonuses and this is not a case where, save in the final year, the husband is said to have contributed more to the home life or welfare of the family than the wife," the judges said.

"In relation to short, childless marriages, where both spouses have largely been in full-time employment and where only some of their finances have been pooled" it may be in the interests of fairness to require a reduction from the equal-sharing principle.

Jonathan Brew, Robin Sharp's lawyer at Harrison Clark Rickerbys, said the ruling "has the potential to open pandora's box" when it comes to advising clients in the future. 

"Where this is a short marriage, questions now arise as to what is a short marriage, and also arise as to what's the value of different contributions," he said. "Also whether there is a different award with one child, or two? Or with a nanny?"

Hohn case

In one of the country's highest profile divorce cases, Jamie Cooper-Hohn, the ex-wife of the Children's Investment Fund Management UK founder Chris Hohn, in 2014 was awarded just 36 per cent of their $US1.5 billion marital estate - still thought to be the largest divorce payout in history.

However, judges in Tuesday's case went to great lengths to say they were not scuttling the more traditional approach to the division of assets.

"Nothing that is said in this judgment is intended in any manner to unsettle the clear understanding that has been reached" on the approach that should be taken in the vast majority of cases, the judges said in Tuesday's ruling.

"The focus of the present appeal, which is very narrow, is upon whether there is a fringe of cases that may lie outside to equal sharing principle."

Julie Sharp's lawyer, David Josiah-Lake, a partner at Josiah-Lake Gardiner, said the ruling was a "a return" to what the law clearly states.

A short marriage "is one factor to take into account because you can't give couples an equal share just because they are married", he said.