A group of British plane spotters, including a Horsham man, were today accused of endangering Greece's national security.

The espionage trial of the 12, who were arrested at an airfield in Kalamata, southern Greece, started today.

They are accused of gathering secret information at air bases and today heard the evidence of the key prosecution witness.

The one woman and 11 men, including Christopher Wilson, 46, of Erica Way, Horsham, were originally charged with planning to pass the information on to an enemy of Greece, which carried a maximum prison sentence of 25 years.

That was later reduced to a "misdemeanour" charge of espionage, alleging they gathered the information but not suggesting they meant to give it to a foreign government.

Squadron Leader Nektarios Samaras, an officer with the Greek Air Force, said the group was seen acting suspiciously at his base in Kalamata, southern Greece.

They were seen writing down details of aircraft and tried to evade being watched by his security officers.

He said: "You went into a restricted area, your movements were suspicious, you did not go as one team but spread out and thus made it difficult for your movements to be observed."

He told the court in Kalamata they were arrested as they tried to leave the base and their notepads, cameras and other equipment were seized.

Sqdn Ldr Samaras said: "The fact that you were moving around a military airport, plus the scanning equipment which allowed you to monitor what was being said in the airport, thus acquiring classified information, could jeopardise the security of the country."

The spotters admit taking notes of the numbers of planes but deny using a scanner which they had with them, which can monitor frequencies used by airports and pilots.

They also deny taking any photographs at Kalamata and insist they were plane spotters pursuing their hobby, not spies.

Later, the trial was told the group were carrying papers stating their hobby was illegal.

Squadron Leader Samaras said print-outs from a Dutch web site were among items confiscated from the group.

Reading from a print-out allegedly found on at least one of the spotters, he said: "It says Greece is an ideal place for plane spotters but unfortunately you are not allowed to take photographs, and taking the numbers of aircraft is a criminal offence.

"It is taken very seriously so be aware of the dangers when you decide to go to the land of the blue seas, Greece."

Mr Samaras said the Kalamata air base was warned that the group was arrested and released at another military airfield, Tanagra, and to be vigilant.

"We had an order to be on our guard because some suspicious people were coming but we are always ready and always alert.

"Our country is a country that could be in danger and we have been especially trained because our country is very vulnerable.

"All security measures were higher because of the bombing of the Twin Towers which had recently taken place."

The group were allowed onto the air bases because Greece was celebrating Air Force Day, when civilians are allowed to go on to the airfields and see some of the planes.

But Mr Samaras said the spotters could not have seen all the planes they recorded from the public areas, and must have used "other measures" to see them.

Asked if he could understand whether the group could have taken the notes as part of their hobby, he said: "I don't understand."

He said he believed the group's notes were too expert to have been made by amateurs and told the court in Kalamata: "It could be that they are using their hobby to take military information."

He conceded most of the information the group had gathered was already available in books and on the internet, but added: "Just because someone has managed to spread it round the world does not mean we don't consider it classified."

The case sparked international outrage last year when the group were held in prison for almost six weeks before being allowed to return to Britain on £9,000 bail each.

Their trial formally began yesterday and Mr Samaras was the first prosecution witness.

Verdicts are expected today or tomorrow.