The UK's terror threat level has been lowered from "severe" to "substantial", which indicates that instead of an attack being “highly likely” they are now categorised as "likely", home secretary Priti Patel informed the House of Commons on Monday (8).

In a written statement to members of Parliament, the cabinet minister said that the change from the fourth-highest to the third-highest of the five-stage categorisation was recommended by the Joint Terrorism Analysis Centre (JTAC) following a “significant reduction in the momentum of attacks” in Europe.

However, she noted that the latest categorisation still indicates that a terror attack remains likely and therefore the public should remain vigilant.

"Substantial continues to indicate a high level of threat; and an attack on the UK is still likely. The public should continue to remain vigilant and report any concerns to the police," said Patel.

"Terrorism remains one of the most direct and immediate risks to our national security… The government, police and intelligence agencies continue to work tirelessly to address the threat posed by terrorism in all its forms and the threat level remains under constant review," she said.

The JTAC, part of the UK's MI5 intelligence service, made its recommendation after an independent analysis last Thursday.

The UK's terror threat levels operate between the highest level of critical, or an attack being imminent; severe, or an attack being highly likely; substantial, or an attack being likely; moderate, or an attack being possible but not likely; and low, or an attack being highly unlikely.

The country's level had been revised upwards from substantial to severe in November last year as a "precautionary measure” following terror attacks in France and Austria, which involved four people shot dead in Vienna, three others dying in a knife attack in Nice, and a teacher murdered in Paris.