Cherie Blair is representing a sanctioned Russian oligarch in a $16bn (£12bn) legal battle with Luxembourg. 

The wife of Sir Tony Blair, the former prime minister, is acting for billionaire Mikhail Fridman in a lawsuit over the state’s decision to freeze his assets in the wake of Russia’s 2022 invasion of Ukraine.

In legal documents seen by The Telegraph, the Russian-Israeli businessman claimed he suffered permanent losses after Luxembourg implemented the European Union’s “spurious and unfounded” sanctions against him. 

The 60-year-old – who was pictured with Mr Blair when signing a deal with BP in 2003 – claimed that Luxembourg took part in an “arbitrary witch-hunt” against wealthy Russian businessmen with investments in the EU under the guise of sanctions.

He argued that this breached a deal Luxembourg struck with the former Soviet Union to protect investors’ assets from being expropriated or nationalised.

Luxembourg is also accused of openly considering transferring Mr Fridman’s frozen assets to help fund the rebuilding of Ukraine after the war. 

Mr Fridman claimed to have been blocked from managing or receiving the returns from $16bn of investments in Luxembourg for nearly two and half years, despite overturning previous sanctions earlier this year. 

Most of Mr Fridman’s assets and investments are managed by companies incorporated in Luxembourg, a financial hub inside the EU.

This includes LetterOne, the investment company which owns health and wellness chain retailer Holland & Barrett. The asset manager is said to have recorded $6.5m in losses as a result of sanctions. 

The Ukrainian-born businessman is demanding compensation for the “fair market value” of the investments before they were frozen.

Lady Blair, who became a barrister in 1976, and her law firm, Omnia Strategy, are among the lawyers instructed by Mr Fridman.

Luxembourg’s government confirmed that Mr Fridman had begun arbitration proceedings against the country. 

A spokesman said: “The Government is currently in the process of analysing the claim and next steps with its legal advisers.”

Mr Fridman has requested that the legal dispute be dealt with in the Hong Kong International Arbitration Centre. 

It comes after the EU’s General Court found in April that there was insufficient evidence that the mogul – who is the founder and main shareholder of Alfa Group, Russia’s largest private bank – and Petr Aven, fellow Alfa Group shareholder, supported the Kremlin’s war against Ukraine.

The ruling applies only to their inclusion on the EU’s sanction list between February 2022 and March 2023. Subsequent sanctions against them remain subject to legal proceedings. He was sanctioned by Britain in March 2022 following the Ukraine invasion, blocking him from accessing his bank accounts. 

Mr Fridman moved to London in 2013 after selling his stake in oil giant TNK-BP to Russian state-controlled Rosneft in a $55bn deal.

This stopped him from paying tens of thousands of pounds towards the upkeep of Athlone House, a London mansion which he bought for £65m in 2016.

He moved to Israel just before Hamas’ invasion last October and was forced to flee to Moscow.

Mr Fridman’s lawyers previously said that he did not intend to return to the UK.

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