Investigators monitoring London Bridge attacker Khuram Butt were not told that his brother-in-law had alerted a counter-terrorism hotline about his behaviour more than 18 months before the atrocity.

A senior counter-terrorism police officer known only as Witness M told the inquests into the victims' deaths that it was "very unsatisfactory" that his team was not informed about the call.

Usman Darr contacted the hotline on September 30, 2015, to report a radical change in Butt's behaviour, as he distributed anti-Western texts and links to jihadi sites, and had become increasingly extreme in his views.

Butt, from Barking, was already under investigation by MI5 and the police for potential attack planning in the UK, but the teams involved were not told about the call and Mr Darr was not contacted.

Counsel to the inquest Jonathan Hough QC asked the witness: "Would you accept that where you have the situation of a family member calling to express concerns about somebody who happens to be under investigation, it's very unsatisfactory that the investigation team doesn't hear of that report?"

Witness M replied: "In short, yes. It denied us, really, the option of discussing that information with MI5, and how it fitted into the bigger picture, and denied us the option of what action to take subsequently to receiving that information."

In the same month Butt was assessed by the security service as a "strong risk" of staging a terror attack on his own, but there was no evidence of attack planning, the Old Bailey heard.

He was found to be "aspirational" in wanting to stage an attack but not having the ability to do so.

Police decided not to charge him with possession of extremist material because there was not a strong enough chance of disrupting any potential terror plot.

Witness M said: "We were still investigating a potential attack. My view was, and is now, that had we moved to arrest him for potential dissemination of extremist material, it was unlikely to result in any significant disruption."

He gave evidence amid tight security, with journalists cleared from Court One and listening by videolink with a camera trained on an empty witness box.

The inquest heard that Butt had associated with members of banned terrorist group Al-Muhajiroun, including Siddhartha Dhar, who went on to fight for Islamic State, and ALM leader Anjem Choudary.

In early 2016, Butt appeared in a Channel 4 documentary called The Jihadis Next Door, although Witness M said he was not "personally aware" of the TV appearance.

Later that year Butt gained work as a doorman and then for London Underground, including working at Westminster station, but no action was taken.

The investigation into his behaviour was temporarily suspended after terror attacks in Paris, the court heard.

In October 2016, Butt was arrested with three others on suspicion of falsely reporting fraudulent activity on three bank accounts, and bailed until January 2017 when he gave a no comment interview to police.

On June 1 that year, prosecutors advised there was not enough evidence to charge him. The court heard that even if he had been charged, he would have remained on bail.

Butt, 27, Rachid Redouane, 30, and Youssef Zaghba, 22, killed eight people and injured 48 others in a van and knife attack at London Bridge and Borough Market on June 3 2017.

The three men mowed down pedestrians on London Bridge before rampaging through Borough Market, stabbing innocent people at random.

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.

The inquest continues.