Three men have been arrested for suspected breaches of the National Security Act, the Metropolitan Police say.
The men were arrested on Wednesday on suspicion of assisting China’s foreign intelligence service.
Counter Terrorism Policing London arrested a 39-year-old man at an address in London, a 68-year-old man in Powys in mid-Wales, and a 43-year-old man in Pontyclun, south Wales.
All three were detained under the Police and Criminal Evidence Act.
They were taken into police custody, where they remain.
Officers have searched the addresses where the men were arrested.
They have also carried out searches at three other addresses in London, East Kilbride, and Cardiff.
Commander Helen Flanagan, Head of Counter Terrorism Policing London, said: “We have seen a significant increase in our casework relating to national security in recent years, and we continue to work extremely closely with our partners to help keep the country safe and take action to disrupt malign activity where we suspect it.
“Today’s arrests are part of a proactive investigation and while these are serious matters, we do not believe there to be any imminent or direct threat to the public relating to this. Our investigation continues, and we thank the public for their ongoing support.”
