UK officials are preparing for a possible court case against Roman Abramovich after he missed a deadline to release £2.4bn he raised from selling Chelsea FC.

The Russian billionaire failed to hand over the money by the deadline of 17 March, amid a dispute over how it will eventually be used.

Government officials said they would now take steps to prepare for a potential court case so the money can be spent for humanitarian purposes in Ukraine. They have written to Abramovich’s lawyers to warn them of this.

They added that they would also increase support for an independent foundation that has been set up to spend the money when it is released.

A government spokesperson said: “We gave Roman Abramovich his last chance to do the right thing. Once again, he has failed to make the donation he committed to.

“We will now take further steps to ensure that the promise he made at the time of the Chelsea sale is kept.”

Spokespeople for Abramovich have been contacted for comment.

Abramovich sold Chelsea in 2022 under pressure from the British government after the Russian invasion of Ukraine. Because he was under sanctions at the time, the government granted him a licence to sell the London club as long as the money was spent supporting the victims of the Ukraine war.

Since then, the two sides have been deadlocked over whether the money should be spent exclusively in Ukraine or whether it can be used elsewhere. The funds are in a UK bank account controlled by Abramovich’s company, Fordstam.

Earlier this week, the Guardian revealed Fordstam’s accounts show Jersey authorities may be investigating whether the money amounts to the proceeds of crime.

Aid charities welcomed the government’s promise to push ahead with preparations for a court case, but warned the delays were already hurting Ukraine.

Bond, which represents development organisations, urged the government to issue a new licence to allow the interest accrued since the 2022 sale – thought to be around £200m – to go outside Ukraine. Ministers have said they are open to this.

Alison Griffin, the head of conflict and humanitarian campaigns at Save the Children, said: “The news that the government is planning to take Roman Abramovich to court to free the Chelsea fund is a significant development.

“However, we are deeply concerned that this will only further delay the release of these much-need funds to help support victims of the war in Ukraine.”