A 37-year-old man has been arrested by counter-terrorism police at an address in Essex.
He was detained in the Harwich area in the early hours of Tuesday and is being held on suspicion of the preparation or instigation of terrorist acts.
His arrest in the town is being linked to suspected extreme right-wing terrorism, according to the Metropolitan Police, which has said there is not believed to be any imminent threat to the public.
The action by the Met’s counter-terrorism command unit is not connected to the murder last month of Conservative MP Sir David Amess in Leigh-on-Sea, Essex.
Officers are carrying out searches at the Harwich location where the suspect was detained and he 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.”
He added: “Officers from across the counter terrorism policing network are working day and night to protect the public from those who might seek to cause us harm.
“The public can really help us with that by getting in touch if they spot something of concern.”