A supervisory authority told the Guardian that plans are allowed to allow thousands of criminals in England and Wales to serve their sentences in the community, otherwise “disastrous consequences” will be sentenced in the community unless the probation service is overhauled.

Martin Jones, chief inspector of probation for HM, said the government plans to oversee criminals from prison to probation, which means the risk of “bringing directly into the community.”

He called for additional funding, more staff, cuts to the retention of traditional Chinese tape festivals and better experienced staff, "Any response to the transition from prison to probation will be invalid at best and at worst dangerous."

His comments were posted after Shabana Mahmood was preparing to announce an overhaul of criminal justice Thursday, after a separate review by former conservative Attorney General David Gauke.

Judges and magistrates in England and Wales will be told to get out of brief detention penalties to support community alternatives, increasing pressure on probation services.

Thousands of criminals are expected to be marked and supervised by probation officials in the community, rather than being imprisoned.

Jones said in a comment ahead of Gauke’s official announcement: “Tomorrow’s independent sentencing review has the opportunity to propose recommendations to rebalance our criminal justice system, ensure that those who commit crimes are properly punished and ensure that our communities are safe – an opportunity must be seized.

“However, if any reform is to be achieved, they must make urgent improvements to address the ongoing failures in probation services, which still bears great pressure. Too few employees, too little experience, managing too many cases, conducting frequent inspections, often revealing significant deficits at work to protect the public and revealing opportunities for missing out on these issues.

Former parole board CEO Jones said the government plan would put the public at greater risk.

"My concern as chief inspector is that unlike prisons, the risk of probation is carried directly in the community, which means avoidable errors can have catastrophic consequences. So any response to the need to simply turn from prison to probation is invalid at best and at worst dangerous."

He said the government must pile up more resources, so have more staff, have more experience and provide better services to address the root causes of crime.

“Detailed attention needs to be given to ensure that probation services are capable of responding to the work required, as well as expertise and funding to ensure better delivery, intervention and outcomes,” he said.

He said that if ministers are going to spend more time monitoring dangerous criminals, ministers must also cut the traditional tape festival and probation.

"The Probation Bureau will need to work more closely and effectively with the police and other agencies to protect the public from harm. Our inspections have found that complex and ineffective systems often prevent probation personnel from effectively communicating and sharing information about risks," he said.

Gauke's recommendations are expected to include allowing prisoners to be free after serving one-third of their sentences under the new minimum and maximum sentence plans.

He will also say that magistrate judges should be encouraged to sentence some offenders up to 12 months, rather than the current six months, and the wider use of extended sentences for pregnant women or people with material dependence should be encouraged.

Reports this week said the government has ordered the addition of tens of thousands of tags that will be used to monitor criminals in the community. Gauke will demand a moratorium on sentences for up to three years instead of the current two-year sentence.

Predictions suggest that prisons can certainly run out of space by November.