"Despite the change in the threat level, terrorism remains one of the most direct and immediate risks to our National Security," Home Secretary Priti Patel said in a statement.
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Britain's terror threat level was downgraded to "substantial" from "severe", the Home Office announced on Monday.
The assessment made by the independent Joint Terrorism Analysis Centre indicates that an attack is still "likely".
Home Secretary Priti Patel emphasised in a statement that despite the downgrade, "terrorism remains one of the most direct and immediate risks to our National Security".
"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," she added.
The last time the British terror threat level was at "substantial" was in August 2014. It was then raised to "severe" because of developments in the conflicts in Iraq and Syria and briefly reached the highest level, "critical", twice in 2017 following the Manchester Arena and Parsons Green tube bombings.
The Manchester Arena bombing — which killed 23 people including the perpetrator — was not the only deadly attack on British soil in 2017.
Five people were killed in March when a man rammed his car into pedestrians on the Westminster Bridge. A further eight people lost their lives in June when three assailants went on a stabbing spree around London Bridge and a man also died two weeks later after being hit by a van near a mosque in north London.
Across the Channel, the Vigipirate terror threat level in France is on "risk of an attack" — the second out of three levels. Germany also considers international terrorism to be "the most virulent threat" to its security.
According to the European Commission, more than 1,050 people were arrested in the bloc last year for terrorist offences with more than 129 failed, foiled or completed attacks taking place.