The Russian oligarch pledged to give the proceeds of the transaction to the people of Ukraine back in 2022 after the government sanctioned Abramovich over his ties to Russian leader Vladimir Putin.
However, the funds are currently frozen in a British bank account, due to a stand-off over how exactly they should be used. This is because Abramovich wants some of the money to go to "all victims" of the war, which would see Russia receive some of the funds.
Now, Starmer has sent a stern message to Abramovich as he demands the funds to be handed to Ukrainian victims.
“The clock is ticking on Roman Abramovich to honour the commitment he made when Chelsea FC was sold and transfer the £2.5 billion to a humanitarian cause for Ukraine.
"This government is prepared to enforce it through the courts so that every penny reaches those whose lives have been torn apart by Putin's illegal war."
Chancellor Rachel Reeves added: "It's unacceptable that more than £2.5 billion of money owed to the Ukrainian people can be allowed to remain frozen in a UK bank account. It's time for Roman Abramovich to pay up.
"If he doesn't act then we are prepared to do what is necessary to make sure that money gets to the Ukrainian people."
Reports state that Abramovich is not expected to make a public statement immediately on the announcement in what is an ongoing story.