A court in Naples has sentenced former Italian premier and media tycoon Silvio Berlusconi to three years in prison for bribing a senator as part of a plot to destabilise a 2006-08 centre-left government.

Berlusconi, 78, will not however have to serve the sentence as the case's statute of limitations expires later this year, well before any final ruling will have been reached on appeal.

"It was a good trial, passionate, but in terms of consequences the imminent expiration date takes all the pathos out of the verdict," said prosecutor Henry John Woodcock on Wednesday.

The case centred around bribes totalling 3 million euros that were paid, through an intermediary, to Senator Sergio De Gregorio in order to get him to leave the coalition of then premier Romano Prodi.

The idea was to further weaken an already fragile coalition and the defection was widely seen as hurting Prodi's government, which collapsed in 2008, two years after it was elected. Berlusconi's centre-right Forza Italia party won the resulting election and he served a third term as Italian premier until 2011.

The senator has admitted accepting the money.

The case marks the latest in a string of legal woes for Berlusconi.

Earlier this year, he completed a community service order for corporate tax fraud but was cleared of having sex with an under-age dancer after judges ruled he could not have known she was a minor.

Berlusconi would have gone to prison for the tax fraud had he been younger but was allowed to serve his time by helping out once a week with dementia sufferers at an old people's home.

In summing up the bribery case, prosecutor Vincenzo Piscitelli had told the court the three million euros paid to the senator were "a colossal economic investment made with the aim of achieving the sole goal that interested Berlusconi, who was obsessed by his desire to kick Prodi out and take his post".