"How has he got on to drugs, where has he got the money to pay for it? He is not supposed to break any laws.
"If he does, then he must go to jail immediately and that is what I want to see. They can't let him get away with it."
The newspaper report said Thompson had received more than £2m-worth of care to help him fit back into society since he and Venables were released and given new identities four years ago.
It was claimed Thompson is getting daily doses of methadone on the NHS and seeing a psychiatrist as an out-patient at a mental health clinic.
Mrs Fergus said: "The fact that Venables has been on Merseyside is a clear breach of his parole.
"I was promised neither of them could ever set foot in the area without me being warned.
"Now he's been to a hospital just down the road, it makes my blood run cold just to think about it.
"I want answers about what has been going on."
She added: "Does the Home Office know about the breaches of parole? Have the probabtion service been covering it up? Do the doctors know who they are treating?"
A Home Office spokesman said: "We do not comment on individual cases."