Darryn Frost fought with Khan and, along with others, pursued him onto London Bridge and pinned him down before police arrived.
Frost, a comms officer for Her Majesty’s Prison and Probation Service (HMPPS), an executive agency of the MoJ, was at the prisoner rehabilitation event in Fishmongers’ Hall near London Bridge when Khan began his attack.
Khan, a guest at the event, was out on licence from prison when he killed Jack Merritt and Saskia Jones, and injured three others.
South Africa-born Frost, 28, told PA news agency how he and his MoJ colleagues were attending the event when he heard a commotion downstairs.
He relayed how he took a narwhal tusk from the wall and, along with another man holding a wooden chair, defended himself and others from Khan, who was brandishing knives taped to both his hands.
In his gripping account, Frost said Khan told him he was wearing an explosive vest and that he and others managed to hold him at bay before the attack spilled out of the Hall and onto London Bridge.
He said: "Along with others, I pursued the attacker, tusk in hand, onto the bridge. We called out to warn the public of the danger and, after a struggle, managed to restrain him to the ground."
"At that point I was trying to isolate the blades by holding his wrists so that he could not hurt anyone or set off the device."
Footage filmed by members of the public shows Frost being pulled off Khan only seconds before the terrorist was shot dead by police.
Call for unity
Frost spoke also of his sorrow that he was not able to save the lives of Merritt and Jones, whose funeral services were held this week.
And he paid tribute to the people who helped him confront Khan as well as the emergency services and members of the public who helped the wounded, putting themselves in danger.
Fost called for the media to use its "amazing ability to connect with people" to help unify the country.
He said: "I feel we all have a duty to challenge the spread of fear, hatred or intolerance within our communities."
The MoJ was contacted but did not wish to comment.
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