British police reveal identities of three London attackers

British police named the third attacker in the weekend terror assault in London, amid mounting anger over how the militant killers had apparently escaped surveillance.

Police identified the third attacker as Youssef Zaghba, a 22-year-old Italian of Moroccan descent, a day after naming his accomplices as Khuram Shazad Butt, 27, a Pakistan-born Briton, and Rachid Redouane, 30, a self-described Moroccan-Libyan dual national. 

Police also said they had made an overnight raid in east London and arrested a 27-year-old man early on Tuesday. Twelve people arrested earlier have since been released without charge.

Butt "was known to the police and MI5" but there was no intelligence to suggest the attack was being planned, the Metropolitan Police said. Zaghba was "not a police or MI5 subject of interest," it added, an assertion that seemed to conflict with accounts in the Italian media.

Criticism immediately flared about how Butt was able to carry out the attack.

He had notably 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.

According to Italian media reports, Zaghba's status as a potential militant was notified to the British and Moroccan secret services. 

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.

Foreign Secretary Boris Johnson acknowledged that the security services had to provide an answer.

"People are going to look at the front pages today and they are going to say, 'How on earth could we have let this guy or possibly more through the net? What happened? How can he possibly be on a Channel 4 programme and then committing atrocities like this?'," Johnson said on Sky News.

"That is a question that will need to be answered by MI5, by the police, as the investigation goes on," he said.

'Not in my name'

In Saturday's attack, three men, wearing fake suicide vests, mowed down pedestrians on London Bridge in a van, before slashing and stabbing revellers in Borough Market, a bustling district of late-night bars and restaurants.

Amaq, an outlet affiliated with the Islamic State 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.

Meanwhile, and in what it said was an unprecedented move, the Muslim Council of Britain said more than 130 imams and other religious leaders had refused to perform the traditional Islamic funeral prayer for the attackers.

A Canadian and a Frenchman were among the dead and citizens of other nations were among the 48 injured, including Australia, Bulgaria, France, Greece and New Zealand. Eighteen are still in critical condition, according to health authorities.