The plane-spotters: Waiting for further hearing
Richard Howitt said he made only "limited progress" during the meeting with Greek justice minister Filippos Petsalnikos, adding that he believed few stumbling blocks had been overcome.
In contrast, Greek foreign minister George Papandreou said progress was being made in speeding up the case.
The Labour MEP is expected to visit the 11 men and one woman during his visit.
The MEP said that he had assurances from Mr Petsalnikos that he would look into the case, Mr Howitt added that the minister insisted that the group had ignored warnings not to photograph military bases.
At an earlier meeting Euro MPs in Brussels condemned the continued detention of the 12 Britons, and two Dutch plane-spotters.
European Parliament president Nicole Fontaine was writing to the Greek government urging a swift end to the detentions.
Cell conditions
Speaking to the BBC on Friday, Greek Foreign Minister George Papandreou said that everyone had to respect the independence of the judicial system in his country.
Of the conditions the group are being held in, he said: "There are no problems there as far as conditions are concerned.".
"We have made sure that they are taken care of properly as everyone should be."
But Mr Coppin said that the group had been strip-searched and thrown into separate cells.
One of the group, Paul Coppin told how the Greek authorities had forced them to sleep on bare concrete floors and had confiscated pills taken for stomach upsets.
"Our situation was bad before, but it is a lot worse now. It is terrifying here. This is hell," Mr Coppin told the Daily Mail.
"This is degrading, humiliating, frightening and terribly unfair. I am a plane spotter, nothing else. I'm not a spy."
The plane-spotters, all of whom deny spying, are expected to spend up to 13 more days in jail awaiting a further hearing - which will be conducted in camera.
They were originally arrested on 8 November for allegedly taking photographs and making notes while attending an air show at a military airfield in the southern town of Kalamata.
Details of one of the most contentious aircraft at the centre of the case, the Embraer EMB, can be found on aircraft spotting websites.