Islamic State has claimed responsibility for the blast, saying a "detachment" from its terror group was responsible.
The military are set to bolster security as police continue their hunt for the Parsons Green bomb "suspects" tonight.
Police said the terrorist threat level remains at "critical", meaning another attack may be imminent.
No one has yet been arrested over the bombing, but anti-terrorism police chief Mark Rowley said the investigation was making "really good progress".
As per the latest updated the British police and the Scotland Yard's counter-terrorism squad, investigating the attack, on Saturday, said that they had arrested an 18-year-old boy caught up doing moves described as insignificant. At least 29 passengers were injured, as several were burned and dozens attempted to escape unharmed.
The suspect was being held for questioning under the Terrorism Act.
"The public should remain vigilant as our staff, officers and partners continue to work through this complex investigation", Basu said.
The news comes after police on Saturday arrested at 18-year-old man in Dover in connection with the rush hour attack.
The arrest of the 18-year-old is coming hours after United Kingdom authorities increased the terror threat to "critical"- its highest level after the London Underground blast that injured more than two dozen people.
The Met said it had spoken to 45 witnesses so far and received 77 images and videos from the public, the BBC reported. Yesterday's bombing was the fifth terror attack in Britain since the beginning of 2017.
"I am sure I speak for London when I say we are incredibly grateful to the police and intelligence services for doing everything possible to keep Londoners safe".
It is not yet known whether the bomb, which was reportedly fixed with a timer, went off at its intended target.