Lawyers called today for new legislation on "co-habiting couples" after the UK's highest court ruled that a man who left his partner nearly 20 years ago was not entitled to half the value of the house they shared.
One expert in family law said the coalition Government should "dust down" plans for law reform. Another said "specific legislation" was required.
Five Supreme Court justices allowed an appeal by hairdresser Patricia Jones against an earlier ruling that ice-cream salesman Leonard Kernott was entitled to 50% of the value of the property in Thundersley, Essex - valued at £245,000 in 2008.
They said Ms Jones, of Thundersley, was entitled to 90% and Mr Kernott, of Benfleet, Essex, should get 10%.
The ruling, which followed a hearing in London, was the conclusion of a three-year legal battle, which had seen lawyers argue in a county court, the High Court, the Court of Appeal and the Supreme Court.
Lawyers said parliament should bring in a new law to provide "certainty".
"This case involved an ordinary couple who were forced to fight through four levels of court," said William Healing, family law partner at law firm Kingsley Napley.
He said: "An overarching law is required, just as exists in Scotland, to protect the weaker party in unmarried couples and to provide certainty. The coalition Government should dust down its plan to introduce law reform that could affect up to four million cohabiting couples in this country."
Marilyn Stowe, senior partner at Stowe Family Law, added: "The fact that four courts have gone through the tortuous process of analysing this case just goes to show why specific legislation for cohabiting couples is required - despite the Government's recent refusal to introduce it. Improved legal rights could avoid any more cases such as Kernott v Jones."
Lord Wilson, one of the Supreme Court justices who considered the case, also spoke of the "continued failure of Parliament to confer upon the courts limited redistributive powers in relation to the property of each party upon the breakdown of a non-marital relationship", in his written judgment.
Mr Healing thought the Supreme Court ruling a fair result for Ms Jones but said the "law remains grey and unclear". Mrs Stowe said the ruling was a "landmark decision" which could affect "hundreds of thousands of families".
In 2008, a county court judge sitting in Southend, Essex, ruled that Ms Jones should get 90% of the value of the house and Mr Kernott 10%.
That decision was upheld by the High Court in London in 2009 but overturned on a majority by three appeal court judges in London in 2010. Appeal judges said there should be a 50-50 split.
Ms Jones had appealed against the Court of Appeal decision to the Supreme Court at a hearing in May.
The Supreme Court today unanimously allowed Ms Jones' appeal and restored the county court order.
Supreme Court justices heard how Mr Kernott and Ms Jones, both now in their 50s, split up in 1993 after sharing the house in Thundersley for eight years.
They were told, at the May hearing, how the couple bought 39 Badger Hall Avenue in 1985 in joint names and taken out a joint mortgage.
Mr Kernott moved out, leaving Ms Jones to continue paying the mortgage, maintain the house and bring up the couple's two children, Lauren and Dean, both now in their 20s.
Judges were told that Mr Kernott had waited until his children were grown before making a claim on his old home.
Neither Mr Kernott nor Ms Jones were at the Supreme Court today to see Lord Walker, Lady Hale, Lord Collins, Lord Kerr and Lord Wilson hand down the ruling.
Later, Mr Kernott said he accepted the ruling and hoped to move on.
"I never wanted 50% - I thought 25% would be a fair reflection of what I had put into the property," he said. "When I lived there, I paid for everything and I completely refurbished the place."
He added: "I have been painted as this ogre who walked out on his family. I love my family, I didn't want to leave but it was made unbearable for me to stay. It's a sad day for men who are left in a similar position to me and it feels like the law will always side with the woman."
Ms Jones's solicitor Ivan Sampson said later: "I've spoken to her and she is absolutely delighted - and I'm delighted for her. It seemed to be that the case was decided on the facts."