But a top counter-terrorism officer defended his colleagues, saying that in nine weeks five plots had been foiled and that the level of terrorist activity was "completely different to anything we have seen for a long time".

Khuram Shazad Butt, 27, was shot dead by police on Saturday night after he and two associates killed seven people and wounded scores on London Bridge and in Borough Market.

He had been known previously to police and MI5, police said on Monday night.

He featured in a Channel 4 television documentary, screened in Britain at the beginning of 2016, titled "The Jihadis Next Door", in which he was filmed unfolding a jihadist flag, praying and arguing with police in a London park.

He was a known associate of notorious hate preacher Anjem Choudary, and a follower of Choudary's banned al-Muhajiroun network.

He worked as an attendant in an all-Muslim gym in east London run by a member of Choudary's network who was alleged to have set up weapons training in Pakistan for the July 7 bombing in London in 2005, The Times reported.

One man told BBC radio that Butt had been part of a group led by Choudary who demonstrated outside parliament the day after another al-Muhajiroun follower murdered British soldier Lee Rigby in 2013.

Butt, who was wearing an Arsenal shirt under a fake suicide vest during the London Bridge attack, was a British citizen born in Pakistan who lived in Barking, east London.

He was married with two children and had worked for a company that manages KFC outlets, for the London Underground and had been the director of a company called Kool Kosmetics.

Several people had reported him to the anti-terror hotline in recent years, and neighbours recalled incidents such as his going to a barbecue and declaring it a "no-women zone". Locals said he had been ejected from a mosque in 2015 for arguing with an imam over whether worshippers should vote.

A police file was opened on him in the northern summer of 2015.

He was the subject of one of the police's 500 active terror investigations, said the Met's counter-terror head, assistant commissioner Mark Rowley.

"All the work done has never provided any evidence or intelligence of attack planning or other serious offences, consequently as time went on prioritisation of that operation moved and was currently in the lower echelons," Mr Rowley said.

He said he had "seen nothing yet" to suggest that a "poor decision had been made" in relation to the investigation of Butt.

On Monday night police identified the second of the two attackers as Rachid Redouane, 30, who had claimed to be Moroccan or Libyan, and also went under a different name - Rachid Elkhdar - with a different date of birth that made him five years younger.

He was not known to police or security services, police said. He was reported to be a pastry chef from Ireland.

"Work is ongoing to understand more about them, their connections and whether they were assisted or supported by anyone else," a Metropolitan Police statement said.

On Tuesday police identifed the third attacker as Youssef Zaghba, an Italian national of Moroccan descent who had been living in east London.

They said he was not a police or MI5 subject of interest.

However Italian newspaper Corriere Della Sera reported on Tuesday that Italian intelligence had reported the man to both Moroccan and British authorities, after arresting him at Bologna airport in March 2016 as he tried to catch a flight to Turkey and then travel to Syria.

Mr Rowley urged anyone with information about the men, their movements and locations in the days and hours before the attack to come forward.

"The police and our partners are doing everything we can across the country to help prevent further attacks and protect the public from harm," he said.

"At any one time MI5 and police are conducting around 500 active investigations, involving 3000 subjects of interest. Additionally, there are around 20,000 individuals who are former subjects of interest, whose risk remains subject to review by MI5 and its partners.

"The security and intelligence services and police have stopped 18 plots since 2013.

"In nine weeks we've had five plots foiled and three successful attacks. That is completely different to anything we have seen for a long time ??? as the prime minister has indicated, we're going to need to do some things differently."

His comments came as a debate over police numbers, and the link between cuts in 2015 by then home secretary Theresa May and the rise in terror attacks, became the hot topic of the British general election campaign.

Labour leader Jeremy Corbyn joined others, including David Cameron's former strategy chief Steve Hilton, in calling for May to resign or be voted out over her record on security.

The UK has 20,000 fewer frontline officers than it did in 2010, a cut that Mrs May has defended as a necessary part of post-financial crisis austerity, justified by falling crime figures.

But London mayor Sadiq Khan said he was concerned about whether police had the resources they need, saying London had lost hundreds of millions of pounds from its policing budget, forcing it to close police stations and lose thousands of staff. He said the Conservatives' plans would mean another ??400 million ($690 million) cut to the Metropolitan Police budget in the future.

"We'd have fewer police officers and all the experts say that one of the ways we counter terrorism is by fantastic policing in the community," he said.

So far police have arrested 12 people - seven women and five men - and searched four properties on Sunday and two more on Monday in relation to the London Bridge attack.

All those arrested in connection with the attack have been released without charge, police said on Monday night.

Metropolitan Police commissioner Cressida Dick said all the recent attacks in Britain had a "primarily domestic centre of gravity".

"We will always be looking to see if anything has been directed from overseas, but I would say the majority of the threat that we are facing at the moment does not appear to be directed from overseas," she said.

Police also gave an update on Monday evening on the attackers' victims. Of the 48 people taken to hospital after the attack, 36 were still being treated and 18 were in a critical condition.