Both were released in 2001 and given new identities, with a legal ruling ordering that new photographs of them should not be published. Thompson has not been heard of since his release. Earlier this year, Fergus, and James' father, Ralph, both addressed Venables' parole hearing, calling for him to stay in prison.
"I've been fighting for justice for James for 20 years now and I will continue to do so. The Parole Board have made the wrong decision," Fergus said.
She had earlier broken the news of the decision on Twitter, adding: "Just don't believe what I've got to go through. Again."
A Ministry of Justice spokesman said: "The re-release of life-licensed offenders is directed by the independent Parole Board once they are satisfied they can be safely managed in the community. They may be recalled to prison at any time for breaching their licence conditions."
- Independent