One of three men arrested on suspicion of spying for China is the partner of a Labour MP, the BBC has been told.
The men, aged 39, 43 and 68, were arrested in London and Wales as part of a counter-terrorism policing investigation under the National Security Act, the Metropolitan Police said in a statement.
There is no "imminent or direct threat to the public", the Met added, and all three suspects are being held in custody.
Speaking in the Commons after the arrests, security minister Dan Jarvis said the UK would not "trade of security for economic access".
As part of the investigation, searches were carried out at locations in London, East Kilbride and Cardiff.
