A man has been arrested in the Harwich area of Essex by the Metropolitan Police’s Counter Terrorism Command unit.
The 37-year-old, who was arrested in the early hours of Tuesday, is being held on suspicion of the preparation or instigation of terrorist acts.
The Met said that the arrest is linked to suspected extreme right-wing terrorism and there is not believed to be any imminent threat to the public.
The arrest is not connected to the murder of MP Sir David Amess, the force said.
Searches are being carried out at the address where the man was arrested and the man remains in custody at an Essex police station.
Commander Richard Smith, head of the Met’s Counter Terrorism Command, said: “I’d firstly like to reassure the local community in Essex and beyond that we are not aware of any imminent threat to the public in relation to this arrest today.
“However, with the terrorism threat level recently being increased to ‘severe’, I would like to remind the public of the need to remain vigilant and if they do see or hear anything suspicious, then please get in touch and report it to us.”