With flags flying at half mast, Britain will fall silent as clocks strike 11:00am (1000 GMT) to remember the seven people killed and dozens injured in the central London attack on Saturday evening.
While Londoners have declared their defiance in the face of terror, bunches of flowers piling up point to a city in mourning less than three months since five were killed outside the British parliament in another attack.
"To the sick and evil extremists who commit these hideous crimes, we will defeat you. You will not win," Mayor Sadiq Khan said to applause during a vigil on Monday.
As Khan spoke, police named two of the three attackers as Khuram Shazad Butt and Rachid Redouane.
"was known to the police and MI5. However, there was no intelligence to suggest that this attack was being planned," the Metropolitan Police said.
A total of 12 people arrested as part of the investigation have since been released without charge.
The announcement that British intelligence services knew of Butt drew immediate criticism.
"There were some red lights flashing, certainly in the case of Mr Butt," Michael Clarke, a fellow at the RUSI defence and security think-tank, told the BBC.
The London attack follows the May 22 suicide bombing at the Manchester Arena by Salman Abedi -- killing 22 people including children -- who was also known to British intelligence services.
"Certainly with Abedi in Manchester and Butt now, it looks as if there were some indications that on the face of it may have been missed and I think that will be a great concern," Clarke added.
As attention fell on Butt's path to extremism, British media reported he featured in a Channel 4 documentary entitled "The Jihadis Next Door" and numerous people alarmed by his views had gone to the authorities.
"Why didn't they stop TV jihadi?" read The Sun front page, while The Daily Mirror asked: "So how the hell did he slip through?"
Prime minister under pressure
After a brief pause following the London attack, campaigning resumed on Monday and the agenda has been dominated by security issues ahead of Thursday's vote.
Prime Minister Theresa May has vowed to crack down on extremist content online, warning the public: "We cannot and must not pretend that things can continue as they are."
But the premier has faced criticism for her record on security in the six years she served as Britain's interior minister before becoming prime minister last year.
Opposition leader Jeremy Corbyn, when asked by ITV television if he backed calls for May to resign, said: "Indeed I would."
Between 2009-2016, the number of police officers fell by almost 20,000, or around 14 percent, according to the independent Institute for Fiscal Studies think tank.
"What they miss, in cutting numbers of police on the beat, as it were, is that community intelligence," Clarke told the BBC.
Corbyn has pledged to hire thousands of officers for neighbourhood duties, arguing that a grassroots approach would curb crime and radicalisation.
But May has insisted London police were happy with their resources and counter-terrorism budgets have been protected.
jpegMpeg4-1280x720There has been widespread praise of the quick response on Saturday from armed police, who killed the three attackers with 50 shots within eight minutes of the alarm being raised.
The three men wore fake suicide vests as they drove a white van into pedestrians on London Bridge, before stabbing revellers in the nearby Borough Market area.
The Amaq news agency, which is affiliated with the IS group, said the attacks were carried out by "a detachment of fighters from Islamic State".
A Canadian and a Frenchman were among the dead and citizens of several nations were among the 48 injured, including Australia, Bulgaria, France, Greece and New Zealand.
Eighteen are still in critical condition, according to health authorities.
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