A plan to merge the probation and prison services could lead to offenders being inadequately supervised, probation officers have warned.
Probation officers say the merger plans are risky
Documents leaked to the Observer suggest Home Office staff are concerned over the planned National Offender Management Service (Noms).
The National Association of Probation Officers (Napo) said the leaked documents "confirmed our worst fears".
The Home Office said the scheme aimed for "robust protection" of the public.
It said that a strategy was in place to ensure Noms had "adequate resources" until 2008 and would benefit from yearly cash increases.
A Home Office spokesman said he could not go into more detail in the run-up to a general election.
The creation of Noms was announced in January 2004, when the government set out its plans for transforming the management of offenders.
But documents passed to the Sunday newspaper suggested the government's own civil servants felt there was a "very high" likelihood that the plans would put the public at risk from violent criminals.
The highly critical assessments were made in the business plan for the National Probation Service for the year ahead.
The civil servants said they felt there was a high likelihood that "loss of key skills" from staff, would result in the "inadequate supervision of dangerous offenders", the paper reported.
Harry Fletcher, Assistant General Secretary of Napo, was critical of Noms and the findings in the leaked document. "It is bureaucratic, it already has a huge centre with 50, 100 staff and as the document says it's full of risks. So there is at least a 90% chance that we'll lose key skills of staff, resulting in the inadequate supervision of offenders," he said.
Liberal Democrat Home Affairs spokesman Mark Oaten said the plan to merge the services was of "grave concern".
"They have both got so many problems that the idea that the solution is to create some kind of merger between the two organisations is ill-thought out at this time, " he said.
He added that the Lib Dems would allocate an extra £20 million a year to boost the probation service.
Conservative shadow Prisons Minister Cheryl Gillan was also critical of the plans.
"Labour's flagship re-organisation of the prisons and probation has been chaotic," she said.
"These internal documents show that there is a serious risk to the public from dangerous offenders being released without adequate supervision."
But Labour hit back, defending the policy.
A party spokesman said the scheme would ensure that "progress made in prison is followed through in the community" and that "cutting re-offending is a top priority for all."