Former Culture Club frontman Boy George was sentenced on Friday to 15 months in jail after being found guilty last month of falsely imprisoning a Norwegian male escort.

Tried under his real name George O'Dowd, the 47-year-old Briton denied the charge of false imprisonment at his London flat in April, 2007.

But the length of the sentence was a surprise to lawyers who had expected a term of around three months, or even a suspended sentence.

"This offence is so serious that only an immediate sentence of imprisonment can be justified for it," the judge said.

He said the escort, Audun Carlsen, was "shocked, degraded and traumatized" at being detained and attacked by O'Dowd and an unidentified companion, and said a guilty plea "would have been true evidence of remorse and saved your victim from ... cross-examination."

The singer had told police he invited Carlsen back to his home after a cocaine-fueled pornographic photo shoot in January, 2007, because he suspected the Norwegian of stealing pictures from his computer.

Carlsen countered that the singer had handcuffed him and beaten him with a chain because he was angry he had refused to sleep with him when they first met.

O'Dowd did not give evidence during the trial, but before sentencing his lawyer Adrian Waterman urged leniency, saying O'Dowd had acted under the influence of illegal drugs, was recovering from his addiction and was a "kind and generous man."