London (AFP) - A former hippy whose ex-husband made a fortune after their 1992 divorce on Wednesday won the right to seek a chunk of his wealth in a landmark British court ruling.

Kathleen Wyatt, 55, wants a Â£1.9 million payout from green energy tycoon Dale Vince -- despite lodging her claim 20 years after their divorce.

Five Supreme Court judges ruled in Wyatt's favour Monday following a hearing in December -- a decision 53-year-old Vince branded "mad", warning it could open the floodgates for claims on relationships which ended decades ago.

The pair met as students, married in 1981 and lived a "New Age Traveller" hippy lifestyle on the road. They had one son.

They separated in the mid-1980s and divorced in 1992. A few years later, Vince founded Ecotricity, which claims to be "the world's first green electricity company", supplying power from renewable sources.

The BBC said Vince started out using a wind turbine he had made to power his caravan, and was now worth an estimated Â£107 million.

Wyatt lodged her claim for "financial remedy" in 2011. The High Court accepted her bid but the Court of Appeal overturned the decision.

Now the Supreme Court -- the highest in the land -- has ruled the case should go ahead in the lower High Court.

Judge Lord Nicholas Wilson said Wyatt's claim was "legally recognisable" and not an "abuse of process".

He said a Â£1.9 million payout was "out of the question" and could even be dismissed -- but the Supreme Court judges thought that there was a "real prospect" that she would get a "comparatively modest award".

The judge said Wyatt had raised their son in "hardship" and the court must have regard "to the contribution of each party to the welfare of the family".

In a statement, Vince said he was "disappointed", given the relationship had ended more than 30 years ago.

"It's been so long that there are no records: no court has kept anything, and it's hard to defend yourself in such circumstances -- indeed the delay itself has enabled the claim, because there is no paperwork in existence," he said.

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"I feel that we all have a right to move on, and not be looking over our shoulders. This could signal open season for people who had brief relationships a quarter of a century ago... it's mad in my opinion."

Wyatt said: "It's an important judgement."

Her lawyer Barbara Reeves added: "Our client has had a very difficult time and we are very pleased."