The UK’s terrorism threat level has been downgraded to “substantial” from “severe”, meaning an attack is now “likely” rather than “highly likely”, the Home Secretary Priti Patel said.
The decision was announced in a written ministerial statement to Parliament on Monday.
In it, she said: "Despite the change in the threat level, terrorism remains one of the most direct and immediate risks to our national security.
"Substantial continues to indicate a high level of threat; and an attack might well occur without further warning.
"As ever, the public should remain vigilant and report any concerns they may have to the police.
"Government, police and intelligence agencies will continue to work tirelessly to address the threat posed by terrorism in all its forms.
"The threat level is kept under constant review."
A review of the terror threat in the UK is carried out independently of the government every six months by a section of MI5 called the Joint Terrorism Analysis Centre (JTAC).
The level of threat is based on intelligence and known terrorist groups.
The level was raised to "critical" in May 2017 after the Manchester Arena bombing and later downgraded to "severe", where it has remained since September 2017.
The Prime Minister's official spokesperson said: "The government, police and our world-leading intelligence agencies will continue to work tirelessly to keep people safe."
However, after the leader of the so-called Islamic State group Abu Bakr al-Baghdadi was killed by US forces, Richard Kemp, former head of international terrorism intelligence at the Cabinet Office, has reportedly warned that security services would be "braced for attempts to avenge his death."