British plane-spotters found guilty of spy charges in Greece have been warned they are unlikely to clear their names through the Greek courts.
Human rights lawyer Mr Stephen Jakobi, of Fair Trials Abroad, said he believed the only option open to them now was to take their case to the European courts.
The advice comes as the 12 plane-spotters arrived back in the UK after six members of the group - and two Dutchmen - were each given three-year jail terms while the others were handed one-year suspended sentences for aiding and abetting.
But Mr Jakobi warned them they should effectively write off an appeal in Greece, and instead concentrate on the European courts.
"I don't believe there is a cat in hell's chance of getting anywhere in the Greek courts," he said.
"I see only one reason for going back, which is to spend as little money as possible on getting the appeal turned down, which is what will happen, before taking it to Europe."
The main problem for the plane spotters was that they could not now afford to conduct an expensive appeal which would inevitably fail, Mr Jakobi added.
The spotters were arrested at the Kalamata air base, in the south of Greece, last year and held in custody for several weeks.
They were freed only on £9,000 bail but forced to return to face charges of gathering secret information.
But defence experts and witnesses called to give evidence said the information was already in the public domain while group members insisted they had permission to be there from the Greek air force.
The verdict was condemned by group members, MPs and even the Government, who said the Greek reaction was "disproportionate".