A Russian businesswoman and her Greek ex-husband have run up lawyers’ bills of £5.5 million during a London family court fight over children and money, a judge has heard.

Mr Justice Mostyn was told that Alla Rakshina and Lazaros Xanthopoulos, who are both in their 40s, had spent the money in less than two years.

He said such an amount spent in such a period was “unprecedented”.

The judge aired his thoughts when considering the latest stage of the dispute at a hearing in London on Wednesday.

“I have never known a case where £5.5 million costs have been run up in … 17 months,” said Mr Justice Mostyn, who is based in the Family Division of the High Court in London.

“It is absolutely unprecedented.”

Mr Xanthopoulos, who represented himself, with help from a friend, at Wednesday’s hearing, wants a payout from his ex-wife following the breakdown of their marriage.

His friend told the judge that Ms Rakshina had links to more than 30 companies and was the “75th richest person in Russia” and suggested that she had run up most of the legal costs.

The judge, who considered a number of legal issues at Wednesday’s hearing, was told that Mr Xanthopoulos and Ms Rakshina had lived in London and been married for 15 years.

Lawyers said the couple’s dispute over money was at an early stage.

Detail of how much Mr Xanthopoulos, who had been represented by lawyers at earlier stages of the dispute, wants to walk away with was not aired at Wednesday’s hearing.

Barrister Simon Calhaem, who led Ms Rakshina’s legal team, told the judge that the issue at the centre of the dispute would be the worth of “resources in Russia”.

Mr Calhaem said Ms Rakshina was paying alimony to Mr Xanthopoulos pending the conclusion of the dispute.

He said Ms Rakshina was not subject to sanctions.

But he said her “salary” was paid in Russia and had reduced from £5,000 a month to £3,500 a month following the outbreak of war in Ukraine.

Mr Justice Mostyn oversaw a private hearing.

He said journalists could attend and said Mr Xanthopoulos and Ms Rakshina could be named in media reports of the case.

The judge said their children could not be named.

A spokeswoman for Mr Xanthopoulos said, after the hearing, that he had been a “house husband” during the marriage.