Those arrested were four men and two women, aged between 23 and 62, police said, adding there was no imminent threat to the public.

“This activity has come about following a significant investigation and operation into activity we believe is linked to the terrorist group PKK,” said acting commander Helen Flanagan.

“These are targeted arrests of those we suspect of being involved in terrorist activity linked to the group.”

The PKK, a rebel group founded in southeast Turkey in 1978 with the aim of creating an independent Kurdish state, was banned in Britain in 2001.

The group has been involved in a 40-year conflict, leading to more than 40,000 deaths.

British police said they were carrying out searches at eight premises across London, including the Kurdish Community Centre in the north of the capital, which is likely to be closed to the public for up to two weeks.

“This investigation and activity is about protecting all of our communities, but particularly those in our Turkish and Kurdish communities,” Flanagan said.

“I would urge anyone who thinks they may have been affected or targeted by those linked to the PKK to get in touch.”