Five undercover police officers from Germany were sent to the G8 protests in Gleneagles to infiltrate activist groups, German police have privately admitted.

The officers took orders from the UK's National Public Order Intelligence Unit (NPOIU), the secretive police division that employed Mark Kennedy to spy on activists across Europe, said Jörg Ziercke, head of Germany's federal police.

Ziercke made the admissions in a private sitting of the German parliament held at the end of January to discuss Germany's involvement in the Kennedy case, Der Spiegel reported.

Kennedy, known to activists as Mark Stone or "Flash", because of his seemingly ready supply of cash, was a regular visitor to Germany and helped organise protests in Heiligendamm, the town near Rostock where the G8 meetings took place in 2007.

According to Der Spiegel, whose reporters claim to have been leaked the minutes from the January meeting, Ziercke admitted that German state authorities had specifically requested Kennedy's presence in Heiligendamm.

At the same meeting, Ziercke was forced to tell MPs that Kennedy worked for three German states during at least five visits to the country between 2004 and 2009. He worked for Mecklenburg-Vorpommern, where the G8 meeting was taking place, as well as Baden-Württember and Berlin.

The agent was working on a contract brokered directly by the German parliament, who deemed him a trusted agent, Der Spiegel claimed.

Ziercke also told MPs at the Bundestag that Kennedy had a long-term lover in Berlin – in direct violation of a law forbidding police officers having sexual relationships while undercover – and that he had been invited to Germany by the authorities to infiltrate the anti-fascist movement.

While discussing the Kennedy case, Ziercke answered questions about German undercover officers abroad. The minutes do not specify how many agents were sent to Gleneagles, but someone present at the meeting told Der Spiegel that Ziercke talked of five being sent to Scotland.

Thousands of leftwing protesters disrupted the Gleneagles summit by paralysing traffic and throwing stones at the police.

Ziercke allegedly said the secret operation in Gleneagles was merely part of a European-wide project to exchange information from undercover operatives working across a number of countries.

He said the police forces in EU member states help each other by sharing information "regarding Euro-anarchists, militant left extremists and leftwing terrorists". This sort of co-operation was also common during major international sporting events, he added, and was widely praised by governments. Ziercke said this exchange programme appeared to be useful tool. Police can only tackle organised and conspiratorial international networks by working just as "internationally and conspiratorially", said Ziercke.

However, he said, police should think again about how to control and monitor these sorts of clandestine operations.

Both the Guardian and Spiegel have already reported that Ziercke told German MPs that the agent committed at least two crimes, but the cases against him were dropped at the behest of German authorities who knew Kennedy's true identity.

Kennedy first broke the law during protests at Heiligendamm. He later committed arson during a demonstration in Berlin at which he set fire to containers, Der Spiegel said. The newspaper said Kennedy's involvement in criminal activity raised concerns that he was working as an agent provocateur and not just an observer - and the fact that investigations into both crimes were shelved suggested police authorities wielded an unacceptable influence over the country's judicial process.

Kennedy spent long periods in Germany and lived with individuals in the anarchist movement during his time in the country. At the same time, he entered 22 different countries across Europe using a fake passport, including Spain, Italy and Iceland – where he helped found the activist movement.

The revelations about Kennedy's role in Germany come despite the government maintaining its refusal to publicly answer a series of parliamentary questions from opposition politicians.

The Bundestag said "operational reasons" prevented them answering any questions about the country's co-operation with undercover police officers from other countries, and Kennedy in particular.

The Metropolitan police, which recently took control of the NPOIU, declined to comment.