Boris Mints and his sons Dmitry, Alexander and Igor are being sued by National Bank Trust, which is 99% owned by the Central Bank of Russia, on behalf of Bank Otkritie, once Russia’s largest private lender before it collapsed in 2017.

Lawyers representing the Mints family – who deny the banks’ fraud allegations – say the lawsuit should be indefinitely put on hold because, if the banks win at trial, any damages could not be paid as Bank Otkritie is under British sanctions.

But the banks say their application is “opportunistic”, describing it as “a transparent attempt” to exploit the fact that Bank Otkritie has been placed under sanctions.

The application represents one of the first legal tests of Britain’s sanctions regime in relation to Russia.

Laurence Rabinowitz, representing Dmitry and Alexander Mints, said in court documents that any money recovered by National Bank Trust will go to the Russian central bank, which must transfer 75% of its profits to Russia’s federal budget.

He told London’s High Court that it was effectively being asked to assist National Bank Trust “in filling the coffers of the Russian state, coffers which the Russian state is using to finance its war in Ukraine”.

He also said National Bank Trust is “subject to the same asset freeze” as Bank Otkritie as it is owned or controlled by Vladimir Putin and the Central Bank of Russia’s governor Elvira Nabiullina, both of whom are subject to sanctions.

However, the banks’ lawyer Nathan Pillow said the Mints family’s case would effectively exclude anyone who is subject to sanctions from having access to the English courts.

National Bank Trust denies it is controlled by either Putin or Nabiullina, Pillow said in court documents. He also said the court can enter judgment in favour of National Bank Trust without violating sanctions.