Addressing the Commons on Wednesday evening, Priti Patel said intelligence officers had upgraded the threat facing members of parliament.
A review by the Joint Terrorism Analysis Centre linked to MI5 was launched after the Conservative representative for Southend West was killed on Friday at a surgery for his constituents.
While it did not find any “specific or imminent threat” to MPs’ safety, Ms Patel said that the threat level to MPs was “now deemed to be substantial” and counterterror police will ensure the “change is properly reflected in the operational posture”.
“While we do not see any information or intelligence which points to any credible or specific or imminent threat, I must update the House that the threat level facing members of parliament is now deemed to be substantial,” she said.
“This is the same level as the current national threat to the United Kingdom as a whole, so I can assure the House that our world-class intelligence and security agencies and counterterror police will now ensure that this change is properly reflected in the operational posture.”
Substantial means an attack is likely, while the lower level of moderate means an attack is possible, but not likely.
The murder of the second MP in five years – after the Labour MP Jo Cox was killed by a far-right sympathiser in 2016 – has sparked concern over the safety of British politicians.