Supreme Court justices are considering whether an 80-year-old businessman and his 68-year-old wife should divorce.
Tini Owens wants a divorce and says her marriage to Hugh Owens is loveless and unhappy and has broken down.
She says he has behaved unreasonably and says she should not reasonably be expected to stay married.
But Mr Owens has refused to agree to a divorce and denies Mrs Owens’ allegations about his behaviour.
He says if their marriage has irretrievably broken down it is because she had an affair, or, because she is “bored”.
Five justices on Thursday analysed rival legal arguments, which revolve around concepts of “unreasonable” behaviour and “fault”, at a Supreme Court hearing in London.
They are expected to produce a ruling later in the year.
Lawyers say the case could have implications for people in unhappy marriages and might trigger a law change.
Lady Hale has expressed concern about current law https://t.co/a0GsLL8ue6— Legal Cheek (@legalcheek) May 17, 2018
Justices have heard Mr and Mrs Owens married in 1978 and lived in Broadway, Worcestershire.
Mrs Owens petitioned for divorce in 2015 after moving out.
She has already lost two rounds of the battle.
In 2016 she failed to persuade a family court judge to allow her to divorce.
Last year three appeal judges ruled against her after a Court of Appeal hearing in London.
They said Mrs Owens had failed to establish that her marriage had, legally, irretrievably broken down and dismissed her challenge to a ruling by Judge Robin Tolson.
One appeal judge said she had reached her conclusion with “no enthusiasm whatsoever” but said Parliament would have to decide whether to introduce “no fault” divorce on demand.
Another said Parliament had “decreed” that being in a “wretchedly unhappy marriage” was not a ground for divorce.
Mrs Owens’ lawyers say she should not have to prove that Mr Owens’ behaviour has been “unreasonable” – only that she should not “reasonably be expected” to remain with him.
They say the case is about “proper interpretation” of legislation.
Mrs Owens is seeking to change the law and introduce divorce on unilateral demandNigel Dyer QC
Barrister Philip Marshall QC, who leads Mrs Owens’ legal team, told justices on Thursday that a “modest shift” of focus in interpretation of legislation was required.
“The evidence of (Mrs Owens) … demonstrates powerfully that the effect on her of (Mr Owens’) behaviour – however culpable – is such that she should not reasonably be expected to return to a married relationship with him,” said Mr Marshall.
“It is submitted that the court can be satisfied … that (she) is entitled to a decree.”
But barrister Nigel Dyer QC, who leads Mr Owens’ legal team, disagreed and raised concern about the introduction of divorce on “demand”.
He said Supreme Court justices should not “refashion” legislation.
“(Mrs Owens) is seeking, in effect, to change the law and introduce divorce on unilateral demand,” said Mr Dyer.
“It is not a proper function of the Supreme Court to dilute or refashion a statute.”
He added: “If the divorce law is to be changed then it is a task for Parliament.”