Two British journalists who were given short jail terms in Indonesia Tuesday for working without correct visas said they were relieved to be going home but disappointed they were treated as criminals for doing their jobs.

Neil Bonner, 32, and Rebecca Prosser, 31, were sentenced Tuesday to two-and-a-half months in prison, less than the five months sought by prosecutors who accused them of misusing their tourist visas to make a documentary about piracy near the western island of Batam.

Unless prosecutors appeal against the sentence, their lawyer said the pair, who have been detained since May, could walk free after time spent in custody awaiting trial is taken into account.

Prosser said it was a "big relief" to be going home but condemned their sentence as a "criminalisation of journalists".

"I think this makes it a more dangerous landscape for other journalists in Indonesia," she told reporters in Batam after the sentence was passed.

Bonner thanked their supporters but expressed sadness because "this is journalism on trial, and we've been found guilty".

"I don't think journalism is a crime," he said.

Presiding judge Wahyu Prasetyo Wibowo said the defendants had violated their visas but admitted their wrongdoing and apologised.

The pair arrived in Indonesia to shoot a documentary about piracy for production house Wall to Wall with funding from National Geographic, according to their indictment.

It added they had hired several Indonesians to act out a scene of a tanker being boarded by a group of pirates off Batam. The island is in the Malacca Strait, a major shipping lane.

Their lawyer Aristo Pangaribuan expressed regret that the prosecution was considering filing an appeal, saying his clients were not bad people who had served their time and would pay the 25 million rupiah fine ($1,850) imposed on each.

"I told the judge I hope the prosecutors are on the same page, because if they file an appeal, whether we like it or not we have to deal with it," he said.

Foreign journalists wanting to report in Indonesia must get a special visa. Those detained in the past for illegal reporting have been deported immediately or given short prison terms.

Two French journalists were given jail terms of two and a half months last year after being caught in Indonesia's Papua province trying to make a documentary about the separatist movement while on tourist visas.