Some 2,300 sex offenders will be among the criminals whose supervision is outsourced to private contractors under government reforms to probation, it was claimed.
Around 3,200 gang members, 8,400 people convicted of domestic violence and 15,900 robbery cases are also among the "medium risk" offenders set for private supervision, the National Association of Probation Officers (Napo) said.
The public will be put at risk if such offenders are taken out of the care of the public sector and transferred to private firms such as G4S and Serco, the union said.
Speaking yesterday, Napo general secretary Harry Fletcher said: "The Government's plans are both chaotic and dangerous."
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His mother Princess Diana was killed in a car crash in Paris in 1997 when he was just 12 and his brother William was 15.
The 21-year-old, who was arrested on Sunday, also allegedly injured two other people in the attack in the German city of Reutlingen.
She was going to the aid of a family member who got out of the car in the middle of the park and was dragged away by a different tiger.