Studies show that the German economy loses around €50 billion a year as a consequence, Burkhard Even, head of the counterintelligence section of the Federal Office for the Protection of the Constitution, told the audience at a recent security forum in Bonn.

The spying is a mix of official, intelligence service agents, and unofficial business spooks, he said.

Even estimated that of the 500 registered staff of the Russian embassy in Berlin, at least 150 were working as intelligence agents, disguised as diplomats or journalists.

He said that more than four million Russians live in the country as a whole, leaving him unable to guess at how many agents might be hidden amongst them.

Russian intelligence services have been instructed by the government to supply their industry with the most modern know-how to save money developing Russian products, one German official told the forum.

Russian firms doing deals with foreign companies have to contact intelligence services before making firm agreements, the forum heard, giving the government agencies control over investments and businesses deals.

Both Russian and Chinese intelligence services are particularly focussing on German companies experiencing financial difficulties, sending agents posing as businessmen to offer sweet deals to firms operating in high-tech areas.

There are around 80,000 Chinese people living in Germany, Even said, many of whom are commercial spies. China is also buying into, or taking over companies completely, in order to get access to new technological developments.

He also described more underhand methods which he said were often employed by agents posing as visiting business delegations or even trainees who might use mini cameras to take pictures in factories, or secretly copy data.

He said the Chinese were mostly active in the electronic sector. Some reports suggest the Chinese intelligence services have up to a million agents across the world collecting technical and business data to support their industries.

Small and medium-sized companies in Germany are the worst protected against such efforts, particularly when they come via the internet, said Even. But the weakest link is always the innocence of staff, he stressed, calling for companies who suspect a spy attack to contact his office.