Stasi scent-tracking methods are being used to keep a check on selected protesters planning to demonstrate at next month's G8 summit.

Scent traces collected directly from everything from people's palm sweat to their vests and cigarette lighters have been made available to investigators so that sniffer dogs can detect potentially violent protesters, federal prosecutors confirmed yesterday following reports in the German media.

"This has happened to several suspects," said Andreas Christeleit, a spokesman for the prosecutors. It is believed that most samples were collected during recent early-morning raids across Germany.

The revelations have immediately led to comparisons with the methods of the former East Germany's secret police, the Stasi, who habitually collected the scents of dissidents to identify suspects at a later date. It was thought that such chilling espionage techniques had been consigned to history.

But the news that similar methods are to be deployed at the upcoming summit in a democratic Germany has further angered activists already fuming over the construction of a 7.5-mile barbed-wire fence around the venue, at Heiligendamm on the Baltic coast.

"[This is] another step away from a democratic state of law towards a preventive security state," said Petra Pau, a member of the opposition Left party. "A state that adopts the methods of the East German Stasi robs itself of every legitimacy."

But according to experts it is as legal as collecting fingerprints. Scientists looking to expand the use of smell banks say it is possible to determine someone's age, their sex and any illnesses they might have through traces of their body odour.

A 68-year-old atomic energy protester from Hamburg, identified by police as a possible danger to the G8 summit, reported how investigators knocked on his door at 8am and demanded scent samples from him.

The man said he was made to hold metal pipes in his hands - as palms give off an immediate scent - which were then sealed and marked with his name before being taken away.

The police have responded to the reports by saying that they are trying to find out the sender of letters confessing to 14 arson attacks in the Hamburg and Berlin areas which are believed to be connected to the anti-G8 movement. They hope that a scent register will help them to do so. Police say they suspect that the same people are planning fire bombs and other attacks on the June 6-8 meeting.

Summit opponents are trying through the courts to lift a ban on a so-called "star march" planned at Heiligendamm on June 7, introduced after an interior ministry decision to prevent protesters coming within five miles of the resort.

The number of car burnings in Berlin has risen considerably over the past fortnight as tension rises, as have incidences of anti-G8 graffiti.