A highly successful businessman from the United States "not willing to pay a penny" in a multimillion-pound divorce battle has been told by a judge that he must share his fortune equally with his wife and hand her around £80m.

Randy Work, a former key executive in Texas-based private equity company Lone Star, had argued in court that she was only entitled to £5m.

Mr Work, 47, said that "unfortunately" the mother of his two teenage children, Mandy Gray, 45, had failed to abide by a Texan post-nuptial agreement.

She was therefore prevented from receiving a more substantial sum, or anything other than the £5m deemed to be her own separate property, an amount expected to fall to just over £3m when bills are paid.

But Mr Justice Holman, sitting in London, disagreed and told him: "Having offered to pay her nothing you now have to pay her tens of millions of (US) dollars."

The judge told Mr Work that he had offered not a penny "and you are going to have to pay her 100m-120m dollars".

The judge, sitting in the Family Division of London's High Court, said the couple had been equal partners in a relationship of more than 20 years.

They married "without a bean" and the husband made his fortune during the course of their marriage while supported by his wife, said the judge.

Mr Work's lawyers suggested he was entitled to a greater share of the accumulated wealth because he made a "special contribution" through his skills at wealth-creating.

But the judge said: "It would, in my view, be unsatisfactory and gender discriminatory now to make an unequal award."

He ordered the first tranche of 60 million US dollars to be paid to Ms Gray within 28 days of his ruling and the whole sum within 90 days.

The judge urged the couple to compromise and agree on a fair division of assets, including antique furniture and modern art, to achieve equal shares and "to stop this terrible conflict".

Earlier, he described the two-week "who-gets-what" hearing as "unedifying and destructive pugilism".

The couple began living together in 1992 and married in California in 1995. They separated in 2013 and have two children, now aged 15 and 12.

The court was told that Randy was "the breadwinner" and Mandy "the homemaker".

In 1997 he was offered a job with Lone Star in Dallas, Texas, and soon afterwards he was offered a post in Tokyo, where the couple lived from 1998 until 2005.

They moved to the UK in 2008 and their matrimonial home has been in London ever since. The marriage broke down in 2013 when Ms Gray began an affair with the couple's physiotherapist, referred to as "Mr H".

After the marriage broke down Ms Gray moved to a flat in Kensington to live with her lover.

The judge said Mr Work was "very shocked and very hurt by his wife's infidelity and affair" and it also caused considerable upset to the couple's two children.

In the witness box, Mr Work described how he had gone to Japan and made billions of dollars for Lone Star, buying up real estate, including troubled golf courses, after the Japanese economy became stuck in a sharp downturn.

He told the judge that Mandy had been "a good wife" over 20 years and "a good mother" and would have been entitled to at least £70 million, the "total sum payable" under the post-nup agreement they signed in October 2000.

But he argued that she was not entitled to any of his money, or any of his property, after coming to court to seek a better settlement.

The judge said today that Ms Gray had won the key arguments. She argued when she gave evidence that Clause V of the addendum agreement in the post-nup gave her "the unfettered right" to seek from the court "any form of financial provision the court has power to order".

She argued that the family wealth was generated during the marriage and there should now be an equal division of the current total net assets.

During the hearing the judge repeatedly told Charles Howard QC, appearing for Mr Work, that he was "really concerned" about the husband's "open" position that he was "not going to pay her a penny".

The court heard that both Randy and Mandy were born in the US but had "expatriated" and both are now resident in London.

Ms Gray told the court that the post-nup was part of the move to separate their assets when her husband first decided to give up his US citizenship to save tax in America.

Mr Work, described in court as a world-class triathlete, denied that was true.

The judge said the cost of the court hearing was approaching £3m and the couple had been well represented by high quality legal teams, but some of the spending had been "profligate and unnecessary".

He included in that category a decision to fly to the UK two American lawyers to advise on matrimonial law in Texas, saying that decision had been unjustified and unnecessary.

The judge also dealt with the efforts of the couple to save tax on their wealth.

He said the post-nup agreement had been part of a strategy to partition the couple's assets and for Mr Work to renounce US citizenship "purely to avoid or save tax" in America.

Mr Work had become a citizen of Grenada, a Caribbean island with which he had no other connection, and later gained Irish nationality which gave him the right to free movement within the European Union as he manoeuvred to keep down his tax exposure worldwide.

The judge said Mr Work had paid low tax in Japan, and since coming to England in 2008 had paid an income tax total of about £100,000 whilst earning several million pounds a year on his investments.

The judge said his estranged wife had now also renounced US citizenship and become a national of the Caribbean state of St Kitts and Nevis.