The German government has written to the British Home Office asking for the Pitchford inquiry into undercover policing to be extended to covert operations by British police in Germany.

The inquiry, which was set up following the revelation that former Metropolitan police officer Mark Kennedy had infiltrated protest groups and entered intimate relationships under false pretences, is currently only set to cover Kennedy’s activities in England and Wales.

But with Germany now following the Scottish government in submitting an official request to be involved in the investigation, pressure is growing to extend the inquiry beyond English and Welsh borders.

The German request also coincides with a letter, published on Friday, in which campaigners threaten legal action unless the Pitchford inquiry is extended to Northern Ireland.

Jason Kirkpatrick, an anti-globalisation campaigner and filmmaker who met Kennedy in Belfast, told the BBC: “Unless the public inquiry’s remit is broadened, for anyone living outside England and Wales, the Pitchford inquiry is nothing but a painful whitewash.”

British police have admitted that undercover officers have infiltrated at least 460 political groups since 1968, including in Germany. Undercover officer Kennedy is known to have been active for several years in a number of German cities including Berlin, where Kennedy – then calling himself Mark Stone – was arrested for attempted arson but never charged.

According to Left party MP Andrej Hunko, one of the parliamentarians who have been calling for the German government to investigate the Kennedy case, British officers were deployed to infiltrate leftwing activist groups such as Youth Against Racism in Europe and Dissent!, a network that mobilised against the 2005 G8 summit in Heiligendamm.

“The British Home Office must disclose which other German groups and movements were investigated and on whose orders,” Hunko said in a statement in which he also called for similar inquiries in Germany.

“We also need a committee of inquiry here in Germany in order to assess all these incidents and closely investigate the operations of undercover agents. This includes German police authorities collaborating within two international police networks working on undercover operations, which have become established outside of official scrutiny.”

Undercover police officers engaged in covert missions abroad currently enjoy a certain degree of immunity from prosecution. While any criminal act they are involved in would be investigated in the country where it is committed, the authority that commissioned the officer is responsible for disciplinary action.

Peter Francis, a former police spy-turned-whistleblower, has said that police officers sent abroad received “absolutely zero schooling in any law whatsoever”.

“I was never briefed, say for example, if I was in Germany I couldn’t do, this for example, engage in sexual relationships or something else.”

According to Francis, information obtained on a covert mission abroad was frequently shared with the Met’s local equivalent.