Anger mounted in Britain Tuesday over how one of the London attackers slipped through the surveillance net as Prime Minister Theresa May came under pressure two days before an election.

Flags at half-mast, Britain was to fall silent at 11:00am (1000 GMT) to remember the seven killed and dozens injured on Saturday night, a mourning ritual now grimly familiar after two previous terror attacks in less than three months.

Police said they carried out a fresh raid in east London overnight hours after naming two of the assailants -- Khuram Shazad Butt, 27, a Pakistan-born Briton, and Rachid Redouane, 30, who described himself as a Moroccan-Libyan dual national. A third is still being identified.

Twelve people arrested as part of the investigation have since been released without charge.

The Metropolitan Police said Butt "was known to the police and MI5" but there was no intelligence to suggest the attack was being planned.

Criticism immediately flared about how Butt was able to carry out the attack, as he had featured in a Channel 4 TV documentary entitled "The Jihadis Next Door" and, according to the British media, numerous people alarmed by his views had gone to the authorities.

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.

"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?"

The conservative Daily Telegraph commented: "While we pride ourselves on being an open and tolerant society, it is astonishing that people who pose such a danger to life and limb should be able to parade their foul ideology on TV with no consequences."

"There were some red lights flashing, certainly in the case of Mr Butt," said Michael Clarke, analyst at the RUSI defence and security think-tank.

"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," he told the BBC.

- May under pressure -

After a brief pause, election campaigning resumed on Monday, with the agenda dominated by security issues ahead of Thursday's vote. 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 also faced mounting 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 and 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," analyst 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.

Analysts say the security debate favours Corbyn, who already seems to have been gaining ground ahead of Thursday's vote.

May had called a snap general election on April 18, little more than two years into a five-year parliament, arguing that a commanding majority would give her a stronger hand in the Brexit negotiations with the European Union (EU).

But the campaign focus switched abruptly from Brexit to social issues, to Corbyn's benefit.

According to a poll published Tuesday by the group Survation, May's lead over Labour has shrivelled to just over a single point -- 41.6 percent to 40.4 percent.

However, opinion polls have a poor reputation for reliability in Britain, where they can be skewed by the country's first-past-the-post voting system.

- 'You will not win' -

Saturday's attack saw three men, wearing fake suicide vests, mow down pedestrians on London Bridge, before slashing and stabbing revellers in Borough Market, a haunt for late-night bars and restaurants.

Praise has been heaped upon the police for their swift response and bravery. An armed unit killed the trio with 50 shots within eight minutes of the alarm being raised.

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".

But London Mayor Sadiq Khan, describing himself as "a proud and patriotic British Muslim," slapped down those who invoked Islam to justify acts of murder.

"You do not commit these disgusting acts in my name," he said to applause at a vigil on Monday.

"To the sick and evil extremists who commit these hideous crimes, we will defeat you. You will not win."

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.

Source: AFP