A new law to tackle terrorist propaganda could be introduced in the wake of the 2017 London Bridge terror attack.
Chief coroner Mark Lucraft QC identified a potential gap in legislation following inquests into the deaths of the eight people killed in the atrocity and their attackers.
Ringleader Khuram Butt, from Barking, had looked at extremist material online, including propaganda from the so-called Islamic State, violent images and sermons from extremist preachers.
He, along with Rachid Redouane, also from Barking, and Youssef Zaghba, from Ilford, carried out the terror attack on June 3, 2017.
The coroner said current legislation means it may be impossible for police or MI5 to act against fanatics even when "the material is of the most offensive and shocking character".
And he suggested a new law could be introduced to tackle possession of the "most serious material glorifying or encouraging terrorism," in a prevention of future deaths report, which identified 18 "matters for concern" when it was published in November.
Home Secretary Priti Patel, responding to the report on Tuesday, January 14, said: "The government accepts this recommendation and is currently considering the necessity for a further offence of possessing the most serious extremist material which glorifies or encourages terrorism."
Mr Lucraft suggested extremist material could be criminalised in the same way as the most offensive pornography.
Ms Patel said talks are ongoing between the Home Office and counter-terrorism police "as to whether there is a gap in the current legislation".
"Our operational partners must have the tools and powers they require to tackle terrorism," she said.
"The government notes the chief coroner's comments regarding the evidence at the inquests, the existence of the offence for a person in possession of a prohibited image of a child, and the perception that the lack of a comparative counter-terrorism offence may sometimes prevent counter terrorism policing from taking disruptive action."
Eight people were killed and 48 others seriously injured when terrorists used a hired van to plough into pedestrians on London Bridge before attacking people at random around Borough Market on June 3, 2017.
Butt, 27, Redouane, 30, and Zaghba, 22, were lawfully killed after they were shot dead by armed police, an inquest jury found.
A separate inquest concluded that Xavier Thomas, 45, Chrissy Archibald, 30, Sara Zelenak, 21, James McMullan, 32, Kirsty Boden, 28, Alexandre Pigeard, 26, Sebastien Belanger, 36, and Ignacio Echeverria, 39, were unlawfully killed.
The inquest heard that police and MI5 did not recognise the threat posed by Butt, despite his association with Islamic State fanatic Anjem Choudary and an appearance in the documentary The Jihadi Next Door.
He was a subject of interest in an active MI5 investigation at the time of the attack.
But the probe was twice suspended due to pressure on resources and the authorities did not pass on tip-offs about his extremism, including one from a family member.
MI5 accepted, in its response to Mr Lucraft's report, that the suspension of priority investigations was a "matter of legitimate concern" but insisted the decisions in Butt's case "were sound".
The security service said it had "reviewed and refined" its processes since 2017 but rejected the coroner's suggestion that investigations could be scaled back rather than halted at times of high demand.
MI5 said: "In light of the flexibility within the suspension process and open investigations, the security service concludes that a new category of scaled back investigation is not required at this point and would not achieve the important aim of properly diverting specialist resource to those investigations deemed to be of the highest priority at the time in order to minimise the risk from attack plans judged to be imminent or which are deemed on the information available to pose the greatest threat to the public."
The coroner also said action should be taken to reduce the risk of rented vehicles being used in terror attacks, which could include automated checking of rentals against lists of SOIs.
But the British Vehicle Rental and Leasing Association said the cost of real-time reporting needs to be considered, while the government said there were "considerable challenges" to implementing such a scheme.
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