Six protesters who broke into RAF Waddington in Lincolnshire, home of Britain's first unmanned drones base, were described by a judge at their trial on Monday as "dutiful people". He said it was only with a "heavy heart" that he found them guilty of criminal damage to the base.

Judge John Stobart ordered the protesters to pay £10 compensation each to the RAF, £75 in costs and a £15 victim surcharge. He said he would welcome an appeal.

The protesters argued that the use of unmanned drones was a breach of international law and accused the government of war crimes.

Susan Clarkson, Christopher Cole, Henrietta Cullinan, Keith Hebden, Martin Newell and Penelope Walker all denied criminal damage to a fence belonging to the RAF on 3 June. They spent over half an hour walking around the base distributing leaflets and taking photographs as well as planting a peace garden of a fig tree and a vine.

Lincoln magistrates court heard that their action led to the base, home to 13 Squadron, which operates the drones, as well as a squadron of airborne surveillance planes, being placed on lockdown until the situation was resolved.

Hebden, an Anglican clergyman, told the court: "The decision to pilot armed drones from Waddington makes RAF Waddington a war zone. It brings the Afghanistan conflict into this country and it puts ourselves in grave danger.

"If this country becomes part of a war zone it makes all of our lives less safe. Our intention was to save lives."

However, District Judge Stobart ruled: "I find, and not without some hesitation, that the lack of proximity or relationship between the defendants and those in Afghanistan who may be either targeted or hit accidentally by these drones is insufficient. I therefore, with a very heavy heart, find all the defendants guilty."

The six, who staged their protest on 3 June to mark International Child Victims of War Day, were detained only after civilian police were called to the base.

Earlier, Michael Treharne, prosecuting, said the accused were seeking to justify their actions on the basis that they were attempting in one form or another to protect property or people elsewhere.

"As a result of the damage [to the fence] people were able to go through and into and on to the base at RAF Waddington," he said. "They were seen variously throughout the morning. Their behaviour was polite. They were no threat. There were no threats of any kind."