The issues have been raised by inspectors who have looked at Warwickshire and West Mercia Community Rehabilitation Company (CRC), and rated the service as "requires improvement".
A report from Justin Russell, Chief Inspector of Probation, also said that work to protect children had caused concern.
In his forward to the report Mr Russell said: "The CRC also needs to improve its approach to keeping people safe. Practitioners are not focusing sufficiently on protecting victims and potential victims, and some aspects of work to safeguard children leaves me with concern.
"A CRC’s role in protecting the public is crucial. However well it is performing against other indicators, in the eyes of the public, the CRC will always, and reasonably, be judged by its ability to manage risk of harm."
The report did outline three of ten areas where the CRC performed well – including the supervision of those sentenced to carry out community service punishment.
Inspectors found wide variation in the overall quality of case management between local teams and said that too little work was done to improve family life and relationships. Drug rehabilitation and testing requirements were also not being implemented consistently.
Mr Russell said: “Individuals being supervised complete too little work to reduce the likelihood that they will reoffend. The right work was delivered at the right time in only half of the cases we looked at.”
Inspectors also found the CRC faced challenges in delivering accredited programmes. Judges and magistrates can order perpetrators to complete these evidence-based programmes as part of their sentence, with the aim of changing their behaviour.
Mr Russell said: “We found individuals faced long waits to start their accredited programmes. It was not uncommon for individuals to wait between six months and a year to join a course for perpetrators of domestic abuse. It is unsurprising to see that only a third of starters completed the course last year.”
The CRC supervises nearly 3,000 low and medium-risk offenders across four counties; Shropshire, Warwickshire, Worcestershire and Herefordshire. It is owned by PeoplePlus, a private company.
The Inspectorate has made seven recommendations with the aim of improving the CRC’s performance.
Mr Russell concluded: “I hope that senior leaders will work quickly to take account of the findings of this inspection They have shown they can deliver in some areas – now they need to deliver across the whole of what they do.”
The report explains how the service had not been meeting targets in ensuring victims are safe.
It concluded that not enough checks were being carried out with domestic abuse units and or social services for the cases that were being looked at.
It states: "Assessment focused sufficiently on keeping victims and potential victims safe in 64 of the 98 cases assessed. Responsible officers in Warwickshire, particularly, were not consistently doing enough to understand the factors linked to risk of harm. This has led to a degree of underestimation about the level of harm posed, especially in relation to children.
"There was enough work to include the views of, and information from, partner agencies in 60 per cent of cases. We expect checks to be initiated with children’s social care services and police domestic abuse units for every case before it is allocated to the CRC.
"However, more than two-thirds of cases had been allocated to the CRC from court without information from the police or children’s social care services. Responsible officers in some LDUs found it difficult to obtain relevant information, and this limits their ability to assess risk of serious harm accurately. It was not always clear if relevant information had been pursued by the CRC, and in some instances, there had been delays in doing so.
"In six cases, the individual had not been seen at all by the CRC. Responsible officers reported that they were not expected to complete an assessment or plan in these cases. They were unaware that it remained incumbent on them to do what they could to manage risk of harm in these cases.
"Restraining orders are not routinely included in case records. In some cases, responsible officers were unsighted on the significance of these, even when the offence involved a breach of these orders."
A People Plus spokeswoman said: "We have considered carefully the recommendations set out in the HM Inspectorate of Prisons report and have submitted a robust and comprehensive action plan to the Chief Inspector. We are committed to meeting our obligations to public and child protection and safeguarding, and to managing any possible risks to known and potential victims.
“We continue to work closely with the Chief Inspector and his team to ensure their recommendations are addressed, and that our team continues to support the rehabilitation of offenders while ensuring the protection of vulnerable members of our community.”