The coroner in the London Bridge inquest has criticised evidence given by relatives of the attack’s ringleader.

Summing up the evidence on Friday, the final day of the inquest, Mark Lucraft QC, the chief coroner for England and Wales, said he was unconvinced by the testimony of Khuram Butt’s family members.

Butt’s brother Saad, his sister Haleema and his wife, Zahrar Rehman, all said they had not realised the extent of his extremism and had seen no signs he was planning an attack.

Under questioning, his siblings admitted that with hindsight, they should have reported him to a counter-terrorism hotline. In the event, the only one who did was Haleema Butt’s husband, Usman Darr, although he did not tell the rest of the family and has since fallen out with them and separated from his wife.

Lucraft said of Butt’s family members: “I have to say, I didn’t find any of them convincing witnesses. Each has accepted that they should now have done more at the time.”

He made a point of singling out Saad Butt, who Lucraft said was in a “different position” to the other family members because he was involved in the Prevent programme as a member of an organisation called the Young Muslim Advisory Group.

Saad Butt said he did not report his brother to authorities because he believed he could monitor him. But Lucraft said: “It seems to me that on the basis of what he accepted he did know of his brother and the worrying views he was espousing he did very little, if anything, to accurately monitor his brother’s movements.”

Families of the bereaved want the inquest to conclude MI5 and the police could have prevented the attack and that authorities should have put measures in place to protect London Bridge quicker than they did.

Three terrorists mowed down pedestrians on the bridge before crashing their rented van and stabbing people in and around Borough Market on 3 June 2017. A further 48 people were seriously injured, 19 of them critically, before the assailants were shot dead by police, approximately 10 minutes after the attack began.

After seven weeks of evidence, in which the inquest has heard details of the savagery of the attackers who hunted people down as a team, but also about feats of heroism by members of the public and the emergency services, Lucraft will deliver his conclusions on Friday afternoon.

The conclusions are awaited anxiously by the security services, police and authorities responsible for protecting the public. Britain’s most senior counter-terrorism officer, the Metropolitan police assistant commissioner Neil Basu, was in court to hear the coroner’s conclusions.

In the families’ submissions through Gareth Patterson QC, they say failures in the investigation meant details of attack planning were missed. Official inquiries cleared the police and MI5 of wrongdoing.

But Jonathan Hough QC, the counsel to the inquests, said in his submission that while errors may have been made by MI5 and the police, “it is impossible to say that any such flaws were causally relevant to the deaths under investigation”.

MI5, which takes the lead in identifying terrorist suspects and plots, denies the attack was preventable.

Authorities also face potential criticism over the failure to install protective barriers on London Bridge after Khalid Masood drove his car into pedestrians on Westminster Bridge in March 2017, killing four people before fatally stabbing a police officer guarding the Houses of Parliament.

Xavier Thomas, 45, a French sales manager, was the first to be killed after being hit by the van and flung into the Thames at approximately 10.07pm. Chrissy Archibald, 30, was then struck and killed by the van while walking on the bridge with her fiance. Those stabbed to death were Sara Zelenak, 21, an Australian au pair, Sébastien Bélanger, 36, a French chef, James McMullan, 32, from Brent, north-west London, Alexandre Pigeard, 26, a French waiter, Kirsty Boden, 28, a nurse from Australia, and Ignacio Echeverría Miralles De Imperial, 39, from Spain, an analyst for HSBC.