The Supreme Court has backed the court's rights to decide a 'fair' split of assets for separating cohabiting couples in a ruling with widespread implications for family law.

The judgment handed down today (9 November) in the long-awaited case Kernott v Jones saw the Supreme Court back an initial county court ruling that a woman who had paid most of the mortgage on a bungalow was entitled to 90% of its value.

A county court judge had ruled in 2008 that Patricia Jones should receive 90% of the value of the property, compared to 10% for her former partner Leonard Kernott. The couple had separated in 1993 after living together for eight years, leaving Jones to pay the mortgage, maintain the house and bring up their two children. The property was acquired in 1985.

Kernott initially sought to claim his interest in the property in 2006. The High Court backed the 2008 ruling, but the Court of Appeal last year found that Kernott was entitled to a 50% share in the property as the couple owned equal shares when the property was acquired and had taken no legal steps to change the position.

The Supreme Court's decision, which found that the county court judge had applied the correct reasoning, will be seen as leaning towards the approach more traditionally seen in divorce cases. In matrimonial cases, the courts have traditionally focused on 'fair' settlements – though critics often argue this judicial approach can lead to unpredictable outcomes.

The ruling, which has broad legal implications for cohabiting couples in England and Wales, has been broadly welcomed by family lawyers but has also led to calls for clearer legislation on the distribution of assets after separations.

Withers family law partner Julian Lipson commented: "The outcome of this particular case was probably entirely fair in the circumstances of this couple, but the judgment is a poor substitute for a more comprehensive review of cohabitation laws where proper legal reform is many years overdue."

He added: "The problem is a political one – successive governments have felt that they might be accused of undermining the institution of marriage if they granted specific 'rights' to the unmarried; therefore, they have been reluctant to touch the topic of legal reform."

Macfarlanes private client partner Edward Reed added: "[The decision] illustrates the extreme difficulty of trying to resolve knotty property ownership issues after the event with either no or disputed evidence, heavily infused with emotion and blame."

He added: "What continues to loom large therefore is the courts' power of appreciation, which all the justices endorsed, albeit on different grounds: some regarded the judge's role as being to infer from facts and courses of conduct what the result should be; others preferred the concept that the court is imputing intentions and an idea of what is fair."

Jones was advised by Ivan Sampson of AI Sampson & Co, with Lamb Chambers' Richard Power instructed as counsel. Kernott was advised by Chris Pinnion of Francis Thatcher & Co, with Andrew Bailey of Trinity Chambers instructed as counsel.

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