Supreme Court justices have been asked to decide whether an 80-year-old businessman and his 68-year-old wife should be allowed to 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 that 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 they still have a “few years” to enjoy.
They are not expected to produce a ruling until later in the year.
Lawyers say the case could have implications for people in unhappy marriages and might trigger a law change.
Justices have heard how Mr and Mrs Owens had 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.
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.
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.
Mr Marshall said: “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.
“It is submitted that the court can be satisfied … that (she) is entitled to a decree.”
He said Supreme Court justices should not “refashion” legislation.
Mr Dyer said: “(Mrs Owens) is seeking, in effect, to change the law and introduce divorce on unilateral demand.
“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.”