Police missed “opportunities galore” to prevent the London Bridge attack, a court has heard.

Inquests into the atrocity have been told how ringleader Khuram Butt had been under MI5 surveillance, was a close associate of hate preacher Anjem Choudary and had appeared in a television documentary on jihadis.

But he was not prevented from launching a terror attack that left eight people dead on 3 June 2017.

Butt, Rachid Redouane and Youssef Zaghba ploughed a hired van into pedestrians on London Bridge before stabbing dozens of people in a rampage around Borough Market that only ended when they were shot dead by armed police.

Gareth Patterson QC, representing the families of six victims, told an inquest that there had been “opportunities galore” to spot the trio were planning the attack.

London Bridge Terror Attack Show all 16 1 /16 London Bridge Terror Attack London Bridge Terror Attack Armed police on Borough High Street as police are dealing with a "major incident" at London Bridge PA London Bridge Terror Attack Armed Police talk to members of the public outside London Bridge Hospital as police are dealing with a "major incident" at London Bridge PA London Bridge Terror Attack Police Officers outside the Barrowboy and Banker Public House on Borough High Street as police are dealing with a "major incident" at London Bridge PA London Bridge Terror Attack Armed Police talk to members of the public outside London Bridge Hospital as police are dealing with a "major incident" at London Bridge PA London Bridge Terror Attack Armed police on Borough High Street as police deal with a 'major incident' at London Bridge PA London Bridge Terror Attack Emergency services near the scene of the incident Screengrab London Bridge Terror Attack People run down Borough High Street as police are dealing with a "major incident" at London Bridge Reuters London Bridge Terror Attack Emergency services arrive at the scene near Borough market at London Bridge Carl Court/Getty Images London Bridge Terror Attack Emergency personnel on London Bridge as police are dealing with a "major incident" at London Bridge PA London Bridge Terror Attack Police sniffer dogs on London Bridge as police are dealing with a "major incident" at London Bridge PA London Bridge Terror Attack A second helicopter lands on London Bridge as police are responding to three incidents in the capital, amid reports that a vehicle collided with pedestrians on London Bridge, Scotland Yard said. Officers are dealing with reports of stabbings in Borough Market, where armed officers attended and shots were fired. They are also at an incident in the Vauxhall area PA London Bridge Terror Attack Police attend to an incident on London Bridge in London REUTERS London Bridge Terror Attack Police attend to an incident on London Bridge in London, Britain Reuters London Bridge Terror Attack A police officer escorts members of the public to safety at London Bridge Getty Images London Bridge Terror Attack Police attend to an incident on London Bridge in London, Britain Reuters London Bridge Terror Attack Police attend to an incident near London Bridge in London, Britain Reuters

He suggested that it would have taken a “significant period of time” for the trio to become so close and trust each other in order to plan an attack.

Mr Patterson said the Old Bailey had heard of several instances where the three extremists were together and that there was evidence of contact between them in January 2017.

All three men attended the Ummah Fitness Centre in Ilford, which was run by a senior member of the militant al-Muhajiroun network who was linked to a network of safe houses for British jihadis and terror training camps in Pakistan.

Butt and Redouane had visited each other’s homes and Butt had possibly been trying to buy a gun, the court heard.

Mr Patterson said the pair were in contact with each other “again and again for months”, including at the gym, by telephone and at a barbecue at Butt’s home weeks before the attack.

Acting Detective Chief Inspector Wayne Jolley, the investigating officer, denied that police had missed opportunities and said officers would have been working with the intelligence they had.

Mr Patterson said three identical knives were bought by Redouane the day after the barbecue, adding: “Any reasonably competent investigation should have been looking at Redouane at this stage, I would submit.”

Det Ch Insp Jolley told the court: “That would depend on the intelligence at that time.”

The inquest heard that Zaghba – who previously told Italian police he wanted to be a terrorist in Syria – had been going to the same gym, had telephone contact with Butt and visited his home.

Footage released of London Bridge victim who used skateboard to fight terrorist

Mr Patterson said: “All of these things, when pulled together, I would suggest, is crying out to be looked at.”

He also told the court that all three men were at the gym in May “in the dead of night, speaking together in the street” in what he described as a “highly suspicious conversation” after dumping their phones.

Mr Patterson said the “classic anti-surveillance technique” showed “the attack planning was there to be detected”.

“A reasonably competent surveillance, I would suggest, would have had Butt monitored up to that point,” he added.

But when Richard Horwell QC, representing the Metropolitan Police, asked the police officer whether there was any evidence of attack planning in the months before the atrocity, Det Ch Insp Jolley replied: “Not that we uncovered, sir, no.”

The Old Bailey previously heard that Butt had been a prominent member of the banned Islamist group al-Muhajiroun since at least 2013.

Described as Britain’s “most prolific and dangerous extremist group”, supporters have carried out atrocities including 7/7 London bombings – which targeted the Tube and buses – and the murder of Lee Rigby. Many of its supporters have fought for Isis, al-Qaeda and the Taliban abroad.

The court heard that Butt’s views were so far “off the scale” that his brother-in-law reported him to a counter-terrorism hotline in September 2015.

The Ummah Fitness Centre in Ilford, where the three London attackers met days before the atrocity (AFP/Getty Images)

A documentary aired in January 2016 showed Butt joining a public prayer towards a black flag associated with Isis, alongside a man who later joined the terrorist group in Syria.

He went to Choudary’s home for dinner while the hate preacher was supposedly under bail conditions ahead of a trial for inviting support for Isis.

Butt was also arrested numerous times, including on suspicion of fraud and for abusing a researcher from the Quilliam counter-extremism think tank in 2016 and calling him an “apostate”.

The court was also told that Zaghba had held extremist views from childhood, celebrating the 9/11 attacks and displaying Isis flags on his Facebook page.

He was stopped by Italian police at Bologna airport in March 2016 on suspicion of attempting to travel to Syria and told them he “wanted to be a terrorist”.

Xavier Thomas, 45, Christine Archibald, 30, Sara Zelenak, 21, Sebastien Belanger, 36, James McMullan, 32, Kirsty Boden, 28, Alexandre Pigeard, 26, and Ignacio Echeverria, 39, died in the attack, which lasted less than 10 minutes.