Police in the UK will now be able to stop, search and detain individuals at UK ports to determine whether they are involved in hostile state activity.
From Thursday, fresh measures will allow specially trained officers to take action in relation to espionage and foreign interference.
The new “Schedule 3” powers are part of the UK’s wider effort to tackle hostile state activity.
Outlined in the Counter-Terrorism and Border Security Act 2019, the powers were created as part of the UK’s response to the Salisbury nerve-agent attack in 2018.
Safeguards including independent oversight by the Investigatory Powers Commissioner have also been put in place alongside the measures.
Home Secretary Priti Patel said the new powers send a “clear message” the Government has zero tolerance for those acting against British interests.
“The threat posed to the UK from hostile state activity is growing and ever changing,” said Ms Patel.
“These new powers send a very clear message to those involved in it that this Government has zero tolerance for those acting against British interests.
“But I am clear more must be done and we are developing new legislation to bring our laws up to date and create new ones to stay ahead of the threat.”