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.
ISIS has claimed responsibility for the explosion at the London Underground at Parsons Green that left at least 29 people hurt after an Improvised Explosive Device (IED) caused a "fireball" on a Tube carriage during rush hour.
Metropolitan Police Commissioner Cressida Dick said: 'London has not stopped after other bad attacks and it will not stop after this one'.
British police say that armed officers are searching a home in a London suburb and evacuating neighbors as a precaution as part of the investigation into the subway blast.
A potential network of terror plotters behind the Parsons Green bombing is being hunted by police as the country braced for a further attack, PA reports. Detectives will also look into the CCTV footage before and after the attack to track movements of those they suspect of involvement.
There were no reports of life-threatening injuries in the incident which is the fifth terrorist attack in Britain in less than six months.
Prime Minister Theresa May put Britain on the highest security level of "critical" late on Friday the blast on the London tube train at the Parsons Green underground station.
Police said 45 witnesses have been spoken to and 77 images and videos have been sent in by members of the public.
With the perpetrator believed to still be at large, the threat level has been moved to critical from severe, which means that a terror attack is due to occur imminently.