Mr Mills denies taking a bribe from Mr Berlusconi
An Italian court has found British tax lawyer David Mills guilty of accepting a bribe of about £400,000 from Italian Prime Minister Silvio Berlusconi.
Mills, the estranged husband of UK Olympics minister Tessa Jowell, was sentenced to four-and-a-half years in jail at a court in Milan.
Mills, 64, was not in court and is expected to appeal.
Mr Berlusconi, who last year passed a law making himself immune from prosecution, has denied paying a bribe.
In a statement, Mills said he was "very disappointed" at the verdict.
"I am innocent, but this is a highly political case," he said.
"The judges have not yet given their reasons for their decision, so I cannot say how they dealt with the prosecutor's own admission that he had no proof.
"I am hopeful that the verdict and sentence will be set aside on appeal and am told that I will have excellent grounds."
The court heard Mills had accepted the money in return for giving false testimony in two corruption trials involving the Italian prime minister.
Prosecutors say Mills then used the money to help pay off a joint mortgage he held with his wife.
Ms Jowell was cleared of any wrongdoing after an investigation by UK parliamentary officials.
Following the verdict, she said: "This is a terrible blow to David and, although we are separated, I have never doubted his innocence."
Mills was one of Mr Berlusconi's consultants on offshore tax havens.
The prosecution alleged the prime minister paid him for not revealing details of offshore companies during two previous trials in 1997 and 1998, in which the lawyer gave evidence as an expert witness.
The charges stemmed from a letter which Mills sent to a British accountant in 2004 in which he said the £400,000 payment came from "Mr B".
He wrote that he had not lied, but had "turned some very tricky corners, to put it mildly" and had "kept Mr B out of a great deal of trouble that I would have landed him in had I said all I knew".
Mills initially admitted having received money from Mr Berlusconi "in recognition" of the evidence he gave, but later said the money had come from someone else.
Mr Berlusconi has denied making any such payment to Mr Mills.
Mr Berlusconi introduced an immunity law soon after taking office in 2008
After being swept into power for a third time last April, Mr Berlusconi proposed a controversial law granting legal immunity to the four most senior office holders in Italy, which includes the post of prime minister.
The bill was passed by both houses of parliament, with supporters arguing that the amendment was needed to allow the top state officials to focus on doing their jobs without legal distraction.
When he leaves office, Mr Berlusconi may become subject to the charges again, as long as they have not expired under Italy's statute of limitations.