Roman Abramovich’s wife Irina has lost out on a potential £5 billion fortune by getting divorced in Russia instead of going through the English family courts.

Her agreement to split with the Chelsea Football Club owner in their native country prevents details of the separation becoming public.

But speculation in London was that Mrs Abramovich may have ended up far short of getting 50 per cent of the £10.8 billion her husband is reputed to be worth.

While some thought she may have received £1.5 billion, James Stuart, a divorce lawyer specialising in Russian clients, was quoted saying it could have been as little as £150 million.

So anxious were the Abramoviches to avoid any leak that their brief statement omitted even to say when the divorce happened or where in Russia the application was made.

Mrs Abramovich appeared well-placed to become the world’s richest divorcée with her choice of property, Old Masters and opulent trinkets from the oligarch’s fortune. His empire was financed from his interests in the former state-owned natural assets of his once-communist homeland, notably oil and aluminium. Nobody has explained exactly how a Muscovite orphan rose from being a black-market toy trader to put the Duke of Westminster in the shade, but he clearly knows how to strike a deal.

The Abramovich property portfolio stretches from the Duke and Duchess of Windsor’s romantic Riviera hidea-way, Chateau de la Croe, to a 42-hectare Moscow estate. Mrs Abramovich will have her pick of the artworks she has been buying quietly since becoming a mature art student in Moscow. Her taste is said to be faultless and she has been collecting Russian paintings. A little extravagance has been to treat her Moscow home to a complete redecoration with French and Italian furnishings every time they have a baby. The fifth child in their 16-year marriage arrived three years ago.

While his wife indulges in shopping trips to Harrods, Mr Abramovich has been treating himself to a fleet of yachts, jet aircraft, helicopters and elite cars. With such a huge personal fortune, he is unlikely to need to sell any to finance the settlement.

The couple met when she was an Aeroflot air hostess and he was an ambitious trader flying abroad regularly for deals. A fellow stewardess said that she had been keen to avoid the poverty that she suffered growing up without her father, according to the biography Abramovich: The Billionaire From Nowhere. “My children will never suffer like that. I will do everything to make sure that they grow up in a well-off family and that they prosper in life.” They married in 1991.

Mr Abramovich and his erstwhile mentor, the oligarch Boris Berezovsky, bought the state oil company Sibneft in 1995 for $100 million, a fraction of its market value, during a notorious privatisation scheme, devised to support Russia’s fragile economy during Boris Yeltsin’s reelection campaign. When Mr Berezovsky fled Russia in 2000 to avoid prosecution by President Putin’s new regime, he sold his stake to Mr Abramovich.

Mr Abramovich went on to sell his tranche of Sibneft to state-owned Gazprom for $13 billion in 2005. The year before, he had liquidated his shares in RusAl, the giant aluminium company, selling out to fellow oligarch Oleg Deripaska for a reputed $2 billion.

He shot to prominence in Britain by buying Chelsea for £140 million in July 2003, lavishing £500 million and bringing in star players.

The assumption is that divorce proceedings took place in Chukotka, the remote region in Russia’s far East where Mr Abramovich is governor. Nine time-zones east of Moscow, Chukotka remains a restricted zone for foreigners and even Russian citizens need a special permit from the governor’s administration to visit.

It offered Abramovich the perfect solution to avoid public scrutiny. Even for Russia, where official information is usually available at a price, Chukotka is difficult for muck-raking journalists to penetrate.

But why would Mrs Abramovich, 39, consent to a divorce in Russia when an English court would almost certainly award her half of her husband’s fortune? She has undoubtedly lost out by failing to get a settlement in England, which uniquely divides spouses’ assets with all the subtlety of a Wimpy bar chef making a banana split.

If anything, the former air hostess is even more allergic to publicity than her husband and may simply have shrunk from the prospect of a grim slug-fest in the High Court in the full glare of the media spotlight.

Catherine Kalaschnikova, a divorce lawyer in Moscow, said: “The benefit of a Russian divorce is that they can keep it private because there won’t be any public records.

“The court documents are kept in the chancelery and nobody except the parties and their representatives have access to it.

“It’s a fast process. It takes about a month if there is mutual consent. You don’t have to give any reason. You can simply state that the marriage has broken down.” Russian law provides for an equal division of all assets acquired during a marriage. Mr Abramovich’s wealth was potentially vulnerable, since the couple were poor when they married and lived initially in her mother’s apartment.

“The biggest problem for a wife in Russia is to prove that her husband has all these assets worldwide,” Dr Kalaschnikova said. “Russia has very few agreements with other countries to gain legal assistance and requests for information simply go unanswered. I don’t know if they split it 50-50 or whether she settled for an agreement to avoid all these headaches.”

The couple’s spokesman said: “Mr Abramovich’s corporate interests, including Chelsea Football Club, are not affected by the divorce proceedings.”

Mrs Abramovich must decide whether to bring their children back to Russia or stay in London and risk bumping into her husband’s young companion Daria Zhukova. The 25-year-old former model is reported to have been studying aromatherapy in London where her father Alexander, an oil magnate, has a home in Kensington, West London.

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