Mills admitted accepting money but said it came from another Italian
David Mills, the estranged husband of UK cabinet minister Tessa Jowell, has lost his appeal against a bribery conviction in Italy.
He was convicted of accepting £400,000 from the Italian Prime Minister Silvio Berlusconi in 1997.
Mills had been sentenced in February to four-and-a-half years in prison for corruption.
The Italian PM had been shielded from prosecution by a law he proposed but judges overturned it this month.
Mr Berlusconi has denied paying a bribe and has said he does not even know Mills.
That defence is likely to be re-examined after Italy's most senior court ruled that Mr Berlusconi's protection from prosecution violated the constitution.
Mills was one of Mr Berlusconi's consultants on offshore tax havens. He was accused of accepting the money as payment for keeping quiet about offshore companies during two previous trials in 1997 and 1998.
Much of the evidence against Mills stemmed from a letter he sent to a British accountant in 2004, in which he said the payment came from "Mr B".
The trial verdict said there was no evidence that the money came directly from Mr Berlusconi.
Mills initially confirmed having received money from Mr Berlusconi "in recognition" of the evidence he gave, but later said the money had come from an Italian shipping magnate.
Speaking after the appeal decision, Mills' lawyer, Federico Cecconi, said the case "does not end here".
"We have strong elements in our favour [that] will bring a change in the sentence", he said.