The group insist they have done nothing wrong
Paul Coppin, 57, is one of the party of 11 men and one woman, held on the order of local magistrates for three weeks in a Greek jail without charge.
He said that if the government had taken a stronger line, they could have been free by now.
"We have had a lot of words, but no action. If there had been some action I really felt we could be out of here," he told BBC Radio 4's Today programme.
"We have now been incarcerated for three weeks with the prospect of it being at least another week before the next stage.
"I don't understand the behind-the-scenes, but it appears that a couple of local people have been able to keep 12 people in prison for three weeks without any charges.
"I would have thought that someone somewhere could have put some pressure to get this changed but there doesn't appear to be any sign of this happening."
He said that when they had been first arrested on 8 November during a display at the Kalamata airbase, they had thought it was a misunderstanding that would be quickly resolved.
"When we were picked up we thought that this was going to be over in a couple of hours.
"We were arrested for taking photographs at a public open day which we hadn't done.
"Then when we came up in front of the prosecutor the next morning, this is when it all went completely haywire because they concocted the espionage charges.
"When they found they had no evidence of any photographs, it was changed to espionage."
He said that they were still all spread out across the prison, despite a promise from the authorities that there would be two of them in each cell.
MEP visit
"Ten of us are still sleeping on the floor. The food is very poor.
"We are extremely unhappy about what has been done to us," he said.
Meanwhile, the only female member of the group has been visited by MEP Richard Howitt.
He met Mr Coppin's wife Lesley, a 51-year-old grandmother, in Greece's only female prison, Korydallos, near Athens.
He passed on a message of love from her husband who he saw on Friday.
The pair have only met briefly since their initial arrest.
The British vice-consul, Sharon Silverwood-Robson, will also visit Mrs Coppin, from Mildenhall, Suffolk.
The MEP for the East of England spent two hours with the male British plane-spotters on Friday and said afterwards there were "grave concerns" about their case.
He and British consul Donald Holder met the 11 British men and two Dutch nationals at Nafplion prison, about 56 miles south-west of Athens.
He asked if he could see a cell in the men's prison - but was refused.
"I did receive assurances from the prisoners that the conditions were reasonable, given the fact that this is a prison."
All the group deny spying charges, which carry a 20-year maximum sentence.
They are expected to spend up to 12 more days in jail awaiting a further hearing, which will be conducted in camera with only lawyers present.
The others in custody are: 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.