Clarke found fame playing Mickey Smith in Doctor Who between 2005 and 2010, and went on to become a successful actor, writer, producer and director.
But his screen career collapsed in 2021 after the Guardian published accounts from several women who had worked with him, alleging sexual misconduct, which he denied.
In August, Clarke lost his libel case against the Guardian, after he sued the newspaper’s publisher.
In September, a High Court judge ruled that Clarke must pay at least £3m of the Guardian publisher’s legal costs.
Clarke, who represented himself at the hearing, told the court he thought the Guardian’s legal costs were excessive and should be reduced.
But he is likely to have to pay even more in total after the Guardian told the court that a conservative estimate of its total costs was £6m.