Armed police and military personnel will be deployed over the weekend with the public asked to remain vigilant in the wake of the Parsons Green bomb attack.
Britain is on the highest terror alert after Prime Minister Theresa May raised the threat level to critical, meaning another attack is expected imminently.
As the manhunt continues, Assistant Commissioner Mark Rowley suggested there may have been more than one person involved stating that police were “chasing down suspects”.
On Saturday police revealed they had arrested an 18-year-old man in the port area of Dover in connection with the rush hour Tube attack on Friday.
On Friday night, Rowley said: “Military personnel have been drafted in to protect national infrastructure sites, allowing additional armed police officers to carry out patrols.
“Communities across the UK can expect to see more officers, both armed and unarmed, on patrol by foot and in vehicles over the weekend. In particular, they will be patrolling at crowded places, iconic sites, transport hubs and ports.
“This may mean disruption for those who are travelling. The public are asked to be patient and plan ahead, allowing time for delays.”
Police are reviewing the security of events across the UK and working with businesses and organisers to make events as secure as possible.
Security checks at events will be enhanced, so people attending events should arrive early and allow extra time for these checks. If you don’t need to take a bag, don’t take it.”
Rowley, the UK’s most senior anti-terror police officer, also urged communities around the UK to be vigilant and report any suspicious behaviour to the police immediately.
“Please do not hesitate, no matter how insignificant you may think the information you have is – please let us decide. It could be crucial,” he said.
Announcing the raised threat level, May said police had asked for authorisation to enact part of the first phase of Operation Temperer – “a well-established plan to provide military support to the police”.
Operation Temperer is being enacted after security experts warned another terrorist attack could be imminent.
The use of the military is believed to allow up to 5,000 troops to be deployed in support of the police.
The plan was activated for the first time on May 23 following the Manchester Arena bombing when the Prime Minister said the police had asked for military support and the request had been approved by Secretary of State for Defence Sir Michael Fallon.
At the time, soldiers were stationed at sites including Buckingham Palace and the Houses of Parliament, allowing additional armed officers to attend events such as the FA Cup Final.
Meanwhile, London Mayor Sadiq Khan also urged people to be vigilant, further confirming that additional officers, including armed officers, would be on the streets.
He wrote on Facebook: “There will also be some military personnel deployed to guard sensitive sites which are closed to the public. Meanwhile, on our transport network, extra staff will be on duty and visible.”