Government proposals to part-privatise the rehabilitation of criminals have been criticised by Devon and Cornwall Police and Crime Commissioner Tony Hogg.
Under the plans announced by Justice Secretary Chris Grayling, private companies and charities would supervise low-risk offenders on a "payment by results" basis.
But fears have been raised that the proposed system could "compromise public protection" while Labour has accused the Government of "taking a reckless gamble with public safety".
Mr Hogg, who could eventually become responsible for commissioning such services in Devon and Cornwall, has now aired his concerns about the proposals.
"My position is very much to support probation," he told members of the police and crime panel. "I'm concerned about splitting probation into high and low risk.
"I am very concerned about the privatisation of probation, but it seems to me that the Government's mind is made up about this.
"I feel the risks are very high here. Probation do a very, very good job and I am concerned about the future."
Consultation on the Ministry of Justice's plans, which would see responsibility for monitoring some 200,000 medium and low-risk offenders move from the public sector probation service to the private sector, was held earlier this year.
Private firms and voluntary groups in England and Wales would have to bid for contracts. They would be paid according to their results in cutting re-offending.
Responsibility for high-risk offenders would remain in the public sector.
In his formal consultation response, Mr Hogg said the "payment-by-results approach is to be applauded".
But, he added: "It is an area of work that embodies large elements of public protection and risk and therefore any reforms should be embarked upon very carefully.
"Great care should be taken on the detail and we would strongly urge government to consult extensively and to trial changes wherever possible in order to ensure that any unintended negative consequences are minimised.
"However, a key observation we would make is that this reform seems largely to be a process whereby the functions of what the probation service do now is simply put out to the market.
"We feel this provides some preconceived restricted frame- works to the method which miss the opportunity to think again about what constitutes more effective rehabilitation."
Some £800 million a year is spent on probation services. However, Government figures show that 47.5% of all offenders released from prison in 2010 went on to re-offend within a year.
Mr Grayling said it was "madness to carry on with the same old system and hope for a different result".
The Ministry of Justice is currently assessing consultation responses. Final reforms are expected to be implemented in spring 2015.
