The terror threat level has been reduced as fresh arrests and raids have been carried out linked to the Manchester suicide bombing.
Troops will be gradually withdrawn from Britain's streets from Monday onwards, having been drafted in to bolster police numbers, Prime Minister Theresa May said.
The Joint Terrorism Analysis Centre (JTAC) increased the terror threat level to "critical" - its highest level - meaning a further terror attack was considered "imminent".
It has now been reduced to "severe", meaning an attack is "highly likely".
Speaking after a meeting of the government's Cobra emergency committee, Mrs May said the decision had been taken after "a significant amount of police activity" over the last 24 hours.
She said: "The public should be clear about what this means - a threat level of severe means an attack is highly likely. The country should remain vigilant."
The massacre at the Manchester Arena carried out by Salman Abedi, in which 22 people were killed, was the worst terrorist atrocity to hit Britain since the July 7 attacks in London in 2005.
The terror threat had been at critical for the first time in a decade.
Mrs May also said Operation Temperer, allowing the military to be deployed to protect key sites, will be rolled back after the Bank Holiday.
She said: "To provide maximum reassurance to the public Operation Temperer will continue to operate until the Bank Holiday concludes.
"Then from midnight on Monday onwards there will be a well planned and gradual withdrawal of members of the armed forces who will return to normal duties."