Rehabilitation orders introduced to drive down re-offending rates have been beset by a catalogue of problems, an inspection report warns.
The probation watchdog found measures included in non-custodial sentences for thousands of criminals are not being delivered properly amid confusion and a lack of action.
Rehabilitation activity requirements (RARs) were rolled out in 2015 and are now used in one in three community or suspended sentence orders.
They aimed to increase flexibility in work to help offenders avoid returning to crime. Courts specify a maximum number of days of activity the subject must complete, with probation services then free to decide how the order is delivered.
The requirements can include anger management, counselling, victim awareness and work to address drug or alcohol problems.
But a report from HM Chief Inspector of Probation Dame Glenys Stacey found that not enough was being done to meet the Government's policy aims.
The bulk of the cases are dealt with by community rehabilitation companies, which were created as part of a controversial shake-up of probation services in 2014.
Dame Glenys said: "These orders have a key role to play in reducing reoffending.
"Government hoped that the new probation companies would use them to do more to rehabilitate offenders, but in fact less than ever is being done.
"So far this has been a triumph of experience over hope, rather than hope over experience.
"We advise Government to consider whether, with changes to probation company contracts, these orders can be made to work well, or whether it is time for a more fundamental rethink."
Inspectors reviewed a number of cases and found "significant shortcomings" and a " noticeable lack of impetus or direction in a good proportion" of them.
In more than one in 10, there had been "no purposeful activity at all", while there were also signs of a reduction in confidence among those handing out sentences.
One District Judge said: "What is clear is that RAR days are meaningless to a defendant. The legislation was far from clear".
There was said to be an inadequate response in cases where convicts did not turn up for appointments, and in some cases a high level of absences was deemed acceptable.
The watchdog said it did not find that sufficient impact had been made on reducing the prospect of re-offending in the majority of cases inspected.
Up to the time of the inspection, more than half of the individuals in cases sampled had complied with their orders satisfactorily.
Of those that had not complied, one-third had been returned to court for breach, one third were re-sentenced for a further offence, and one-third should have been returned to court for breach or variation of the order but were not.
A Ministry of Justice spokeswoman said: "Public protection is our top priority, and we have been clear we expect providers to improve their use of this vital tool in order to reduce re-offending, cut crime and keep the public safe.
"We closely monitor the use of RARs and have issued new guidance on how they should be used to support offenders, and given greater clarity to the outcomes we expect to see.
"We are also working closely with courts to raise their awareness of the activities available to them to help offenders turn their backs on crime."
A review of the probation service is due to be completed in April.