Anzhelika Khan was made subject to British sanctions in April 2022, a month after her husband German, who co-founded investment group LetterOne and whose net worth is estimated at $8.4 billion by Forbes magazine.

She argued she had no involvement in Russian politics and held no influence over the Russian government, meaning it was unlawful to subject her to sanctions.

But Judge Sara Cockerill dismissed her case in a written ruling, saying the sanctions were capable of serving the purpose of "sending a signal to Ms Khan and via her to the government of Russia and the international community ... that the UK does not accept acts which destabilise the Ukraine".

Anzhelika Khan's lawyers and Britain's Foreign Office did not respond to a request for comment.

The case is the latest unsuccessful attempt to overturn British sanctions, with the courts previously emphasising the importance of the political aims of the sanctions regime.

The Court of Appeal is due to rule next week on a case brought by Eugene Shvidler, a billionaire ally of Roman Abramovich, in the first substantive appellate test of British sanctions imposed following Russia's Ukraine invasion.

'PROBING QUESTIONS'

Helen Taylor, a legal researcher at pressure group Spotlight on Corruption, said the ruling "poses some probing questions about how individual designations are delivering the government's ultimate aim of deterring Putin".

"While the courts are rightly reluctant to second-guess the government's calls, far more rigorous review is needed of how sanctions are operating, from designation strategy to licensing decisions and enforcement follow-up," she added.

In her ruling, Cockerill noted that German Khan had, over a period of years, given his wife "very substantial gifts, including his shares in four properties and financial gifts totalling some hundreds of millions of pounds".

One gift, which Cockerill said "represents a significant proportion of the amounts given over the years", was given just before German Khan was sanctioned in early March 2022.

She added: "There are also real questions about whether there has been a meaningful investigation into the huge transfer of wealth that German Khan made to his wife just before sanctions hit."

(Reporting by Sam Tobin; Editing by Kate Holton, Kylie MacLellan and Nick Macfie)

By Sam Tobin