A Swedish tech consultant accused of selling sensitive information about truckmaker Scania and Volvo Cars to Russia went on trial in Sweden on Thursday, the country's first espionage trial in 18 years.

The 47-year-old man, whose name has not been disclosed, is accused of espionage and illegal intelligence gathering that put Sweden's national security at risk, prosecutors said.

The accused was arrested in dramatic fashion in February 2019 while dining at a restaurant in central Stockholm with a Russian diplomat suspected of being an intelligence officer.

The diplomat was briefly detained but released on account of his diplomatic immunity.

The arrest led to a diplomatic row between Sweden and Russia, with Stockholm subsequently denying visas to two Russian envoys. Moscow responded by expelling two Swedish diplomats.

At the time of his arrest, the consultant had just received 27,800 kronor ($3,355) for passing information to Moscow, prosecutor Mats Ljungqvist said in February.

The information regarded "manufacturing, such as source codes and construction of products in the automotive sector".

According to the indictment, the man illegally transferred material from his work computer to his private computer and thereafter to USB memory sticks.

In order to hide his activities from being logged by the IT system, he also photographed material from the screen of his work computer.

The trial is expected to conclude on September 1, and the accused risks a maximum of six years in prison if convicted.

In its latest annual report published in 2020, Sweden's intelligence agency said Russia, along with China, posed the biggest intelligence threat to the Scandinavian country.

According to public broadcaster SVT, this is the first time a person has gone on trial in Sweden for espionage in 18 years.