Detectives are also continuing to appeal for witnesses to the incident itself and have also released images of the white Renault van, registration plate number HN66 TKX, used by the three men to carry out the attack.
London Metropolitan Police's Counter Terrorism Command conducted a raid in east London that resulted in the arrest of a 28-year-old man on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism.
In a rare glimpse into the weeklong investigation, police released details on Saturday that showed Butt originally tried to rent a 7.5-tonne truck.
As arrests continue to mount, investigators released new details about the planning and methods of the three attackers and their van and knife rampage. "If you know anything about these particular types of knives, please let us know - it could prove a crucial lead in our investigation". Police shot the attackers dead.
Police believe the intended atrocity was on a similar scale to that in Nice, France, in August 2016 when a truck drove into a crowd and left 86 people dead.
Among the outlets taking part are restaurants around Borough Market, where attackers stabbed five people to death after mowing down pedestrians on London Bridge, killing three.
The three terrorists had tied 12 inch (30cm) pink ceramic knives to their wrists and had petrol bombs in the van.
After his payment was declined, Butt and his two accomplices rented a smaller van that they used to plough into crowds before they went on a stabbing rampage in an attack that left eight people dead and almost 50 people injured.
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"When I come back to Butt trying to get hold of a 7.5-tonne lorry - the effect could have been even worse", Commander Haydon said.
Police discovered 13 wine bottles containing flammable liquid with rags stuffed in them, essentially Molotov cocktails, and blow torches to ignite them, potentially meant for another wave of attacks.
Also inside the van were of office chairs and a suitcase which police say had been stacked inside the vehicle as a cover story to their families to explain why they had hired the van.
Commander Haydon continued: "Many witnesses we've spoken to have provided extremely helpful accounts of the attack but we are still missing pieces of the picture".
Although Islamic State militants have claimed responsibility for the attack, Haydon said there was no evidence the attackers - Pakistani-born Briton Khuram Butt, Italian Youssef Zaghba and Rachid Redouane who had links to Libya, Morocco and Ireland - were directed by anyone else, either in Britain or overseas.
This is stated in the statement of the British police.
She said that includes "whether you see something suspicious, you know somebody who has started to behave strangely, you are hiring a vehicle to somebody and you have concerns about them".
He said Redouane's home - an apartment in Barking, east London - was the safe house where the men put their plot together.
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