The group have been in custody for nearly five weeks
Three judges are due to meet on Tuesday morning in the town where the group were arrested, to decide whether they should be freed or face charges.
Earlier, lawyers acting for the Britons had said they could be released by the end of the week, following the submission of a long-awaited report detailing the evidence against them.
But in the 30-page document, sent to the court on Monday night, the prosecutor recommended they all remain in jail.
The group's lawyer, Iannis Zacharias, dismissed arguments in the report seeking to back up the initial allegations as "wholly amateurish".
On Tuesday, he will ask the court for time to call expert witnesses who say it is ridiculous to regard the plane-spotters as spies.
The prosecutor's report was submitted as UK Foreign Secretary, Jack Straw, renewed appeals to Greece to release the group.
Long wait
"Nothing would please me more than if they were released in the next few days - but I do not want to raise the hopes of people detained," he said.
Mr Zacharias had said the group could be released by Friday if the judges decided to drop the case.
The 12 British and two Dutch plane-spotters had been waiting since last week for the report to be submitted.
The group was arrested on 8 November at a Greek air show and accused of taking photos and notes.
They have appeared once before an investigative magistrate.
'Sinister' visit
Over the weekend it was revealed that Greek Government officials had asked Turkey to reveal anything it knows about the group - especially its leader Paul Coppin.
Friends and relatives of Mr Coppin have admitted that he went to Turkey in May as a guest of the Turkish military, but denied that implied anything incriminating or sinister.
Mr Coppin, 45, whose company Touchdown Tours took the group to Greece on a plane-spotting trip, has said he was in Turkey as an accredited aviation journalist.
British officials accept that the Greek Government is restricted by the separation of authority between politicians and the judiciary.
"It is not possible for ministers to order the judiciary around," said Mr Straw.
But he added that he hoped the "high level" charges of spying would soon be reduced.
"These people have had a very harrowing time indeed - particularly Mrs Coppin, who is isolated from the others.
"The Greeks are in no doubt about the strength of our feeling on this issue."
Christmas concerns
One of the British plane-spotters said he feared they would remain in jail over Christmas.
Wayne Groves, 38, told the BBC: "On 20 December the courts pack up for Christmas until 7 January, which is obviously causing us concern."
He said three of the group were separated much of the time.
The group are trying to keep their morale up with quizzes, books and managed to watch Sunday's Premiership match between Arsenal and Aston Villa on television.
The 12 in custody are Paul Coppin, 45 and Lesley Coppin, 51, of Mildenhall, Suffolk; Peter Norris, 52, of Uxbridge, west London; Antoni Adamiak, 37, of London; Andrew Jenkins, 32, of York; Wayne Groves, 38, of Tamworth; Michael Bussell, 47, of Swanland, near Hull; Michael Keane, 57, of Dartford, Kent; Steven Rush, 38, from Caterham, Surrey; Christopher Wilson, 46, who lives close to Gatwick Airport; Graham Arnold, 38, from Ottershaw, Surrey; and Gary Fagan, 28, from Kegworth, Leicestershire.