He laughed as man beat boy they abused.
Reacting to yesterday's police and NSPCC report on the abuse scandal, he said: "I'm shocked by the amount and the time it's gone on and the amount that's gone on. I'm lost for words."
Mr Cook has now spoken to the police about the second man who abused him after Savile.
He told presenter Victoria Derbyshire: "The man walked into the room and carried on the abuse. He made me do stuff to him and he physically abused me as well, he hit me."
Mr Cook went on: "People have asked me, a couple of friends who know about it now have asked me, why I didn't say it all at the time. My parents are listening to this now.
"How can you tell your mum and your dad that you were forced to give oral sex to somebody and then they physically hit you afterwards, and Jimmy Savile there laughing? "But I'm no longer scared now, and if the police find him I'm going to face him and I will get some justice."
Paralysed Caroline Moore, now in her fifties, has previously claimed Savile abused her as she recovered in the children's ward at Stoke Mandeville Hospital in 1971 following an operation to fuse her spine.
Ms Moore said: "I find it quite scary that people who had the power to stop him didn't use that power and stop that man and he went on to do the most horrific things to people in the most awful circumstances."
Asked why nothing was done, Ms Moore said: "It could have been because he was raising as much money as he was and the hospitals feared they would lose the money. But there were also those who feared him because he had so much power."
She added: "I'm absolutely furious that he was able to do what he did, to the children that he did it to, and nobody would stand up and stop him."
Sylvia Edwards, who said she was assaulted by Savile as he presented Top of the Pops in the 1970s, when she was 18, told the broadcaster: "I'm glad that it's all coming out because people knew about it and they just didn't do anything.
"'I'm glad that a lot more people have come forward."