MPs now face a "substantial" threat level - meaning an attack is "likely" - following the killing of Sir David Amess, Home Secretary Priti Patel has said.
In a statement to the House of Commons, Ms Patel said there had been a "change in risk" after an independent review by the Joint Terrorism Analysis Centre (JTAC) in the wake of the fatal stabbing of Sir David.
It is understood that the threat against MPs was previously deemed to be "moderate", meaning an attack is "possible but not likely".
The JTAC divides threat levels into five categories; low, moderate, substantial, severe and critical.
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Conservative MP Sir David Amess was killed at a constituency surgery in Leigh-on-Sea, Essex
"While we do not see any information or intelligence which points to any credible, specific or imminent threat, I must update the House that the threat level facing members of this House is now deemed to be substantial," the home secretary told MPs.
"This is the same level as the current national threat to the UK as a whole."
Ms Patel said she would ensure that security and intelligence agencies, as well as counter-terror police, would see the change "reflected in their operational posture".
She also urged MPs to "take this change in risk seriously" and to access the range of security provisions and support available under Operation Bridger - a nationwide police effort to enhance the security of MPs that was set up in response to the murder of Labour MP Jo Cox in 2016.
"As well as for our own sake, we have a duty of care to protect our staff and the general public," Ms Patel added.
"I know that every single member will take, register and act upon the advice that is given to help keep ourcountry safe from terror and, of course, enable our own conduct when it comes to making sure that democracy is defended and protected."
Sir David was stabbed to death last Friday as he held a constituency surgery - where MPs' offer face-to-face meetings with constituents - at Belfairs Methodist Church in Leigh-on-Sea, Essex.
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In resoponse to Ms Patel's statement, Labour's shadow home secretary Nick Thomas-Symonds said: "I know that in the face of such unspeakable hatred we stand united and unshakeable in this House, that those who use violence in an attempt to divide us shall never win and we refuse to be intimated by these dark forces.
"And yes, that goes for the vile individual or individuals who erected a noose in Parliament Square today."
JTAC is based at MI5's headquarters in London and is comprised of representatives from 16 government departments and agencies
It brings together counter-terror experts from the police, government and security agencies.
The UK's national terror threat level dropped from "severe" to "substantial" in February.
At the time, Ms Patel said the lowering was due to "the significant reduction in the momentum of attacks in Europe since those seen between September and November" last year.