27-year-old Butt had ganged up with two other accomplices to carry out the terror attack on June 3 that killed eight persons and injured almost 50. He is a 33-year-old man arrested on a street in Ilford, east London, yesterday on suspicion of possession with intent to supply controlled drugs, and further arrested on suspicion of firearms offences.
The Metropolitan Police say the London Bridge murderers attempted to hire a seven-and-a-half tonne truck to carry out their killing spree, but the three men failed to provide correct payment details so used a smaller vehicle.
A safe house in Barking, east London, discovered by police contained a copy of the Koran opened at a page describing martyrdom, equipment for making petrol bombs, and plastic bottles and duct tape for constructing fake suicide bomb vests.
Butt had been warned by police on two occasions - once for fraud in 2008 and once in 2010 for assault. "I urge all Londoners to do what they can to support this appeal and show the world that we are city that will never be divided or cowed by terrorism".
Had the Pakistani-origin London Bridge attacker succeeded in hiring a 7.5 tonne truck, the number of casualties in the carnage would have been much higher, the British media reported on Saturday. Armed police shot dead the three attackers just eight minutes after the first phone call from the public.
Headteacher at Al-Noor Primary School, Green Lane, Goodmayes, Someera Butt is shaken and shocked by the London Bridge terror attacks but confirmed that pupils at her school had not been targeted.
Five other men, aged 27-30, remain in police custody, with 12 others released without charge in connection with the latest terror attack on London.
In the attackers' van detectives found 13 wine bottles, filled with lighter fuel with rags wrapped round them to make Molotov cocktail petrol bombs.
Officers said it appeared the men originally planned a rampage that echoed a similar atrocity in Nice, France. Once across they turned around and travelled back the way they came, before turning around at the top and setting off on their final deadly journey, ploughing into pedestrians as they went.
Investigators also found gravel bags, which also could have been part of their cover story, or may have been "used to weigh the vehicle down", making it heavier and giving it more force.
Police said Khurum Butt, the ringleader, made a booking with a haulage company, but the rental was cancelled when he failed to make the payment on time.
The men jumped out clutching the ceramic kitchen knives.
"There was no evidence uncovered of any attack-planning in relation to him", Haydon said.
She said: "At the present time I do not regard what I have seen as an intelligence failure, but everybody would expect us to look at what has happened and to ensure that both we learn everything that we can, and that we improve and improve and improve".
Ms Dick said the threat to London and the United Kingdom is one many other countries are facing and remained defiant when asked about the future.