Senior judges are to decide whether an ice-cream salesman who left his partner nearly 20 years ago is still entitled to half the value of the house they shared.
Lawyers say the ruling could alter the legal landscape for unmarried couples arguing over property after separating.
Five Supreme Court justices yesterday heard how Leonard Kernott (51) and hairdresser Patricia Jones (56) split up in 1993 after sharing a house in Thundersley, Essex, for eight years.
The hearing at the Supreme Court in London was told the couple bought 39 Badger Hall Avenue, valued at £240,000 in 2008, in 1985 in joint names and had taken out a joint mortgage.
Mr Kernott moved out, leaving Ms Jones to pay the mortgage, maintain the house and bring up their two children.
Last year the Court of Appeal decided Mr Kernott was still entitled to half the value of the house because the couple owned equal shares when they separated.
One appeal judge, Lord Justice Wall, said the case was a “cautionary tale” which all unmarried couples contemplating buying homes should study.
Yesterday, Ms Jones appealed to the Supreme Court against the Court of Appeal ruling.
The judges reserved judgment to a date to be fixed after hearing argument from lawyers representing Mr Kernott and Ms Jones.
They were told Mr Kernott, now of Benfleet, Essex, had waited until his children were grown before making a claim on the home.