Nearly one in ten probation hostels where England and Wales’ most dangerous offenders live after leaving prison have been closed after a staffing crisis.

As ministers prepare the early release of thousands of inmates in September, a leaked memo revealed that “staffing challenges” have led to temporary closures of the heavily-supervised “approved premises”.

The Ministry of Justice (MoJ) has confirmed that nine out of 105 approved premises are currently closed. Untrained security guards are sometimes having to fill in for probation staff, officials have confirmed. It is not clear when any of the closed hostels will reopen.

The developments come after the government refused to rule out the early release of violent rapists and paedophiles among 6,000 men to be released in early September.

In response to the findings, Martin Jones, the HM inspector of probation, said the public was being put in danger by closures of approved premises and failing to ensure they had properly trained staff.

“Approved premises are the place where the highest risk individuals go after release and it is vital that as many places are there for them and you have to get the right staff in place.

“If you have security guards doing their jobs, there is a big risk of things going wrong and the public being put in danger. The government has to get this right,” he said.

Approved premises, or probation hostels, supervise about 2,000 criminals across England and Wales considered too dangerous to release back into the community.

Residents often have drug and alcohol problems and complex mental health needs. They live in the hostels for about eight to 12 weeks, and can be recalled to prison if they refuse to submit to drug and alcohol tests or have their rooms searched.

Staff are required to monitor residents with rapid enforcement action needed to stop violent incidents, self-harm and overdoses.

Insiders, however, said high stress levels coupled with the expiry of contracts with private companies Sodexo and OCS, which provided overnight staff cover at the hostels, had led to a staffing crisis.

A probation manager said: “They’ve known this was coming for 18 months, we’ve not been supported to put staffing in place. The closures mean dangerous men don’t get beds, somewhere someone will get hurt because they didn’t get a hostel bed.”

Another insider said: “There is no room for mistakes, you are surrounded by high-risk people, many of whom are trying to harm themselves or others. It is stressful and leads to many staff taking time off with stress-related illnesses.”

Senior civil servants have been made aware of staffing problems at approved premises. In an email sent to staff in May, Michelle Jarman-Howe, the interim director general of operations at His Majesty’s Prison and Probation service (HMPPS) wrote: “I want to acknowledge the recent staffing challenges which, at times, have led to the temporary closure of some approved premises. I know how hard colleagues have worked through this period often stepping in at short notice and going above and beyond to maintain safe services.”

The probation officers’ union Napo sent a questionnaire to 21 staff working in hostels last month. They found that 16 had witnessed security guards covering work usually conducted by probation staff.

Napo’s general secretary, Ian Lawrence, said: “We are seeing further closures due to an estate not fit for purpose, lengthy delays in vetting new staff and a badly managed process to bring private provider staff in house.

“Our approved premises estate needs significant investment if it is to provide the very much needed accommodation for high risk of harm people coming out of prison.

“The use of security guards to fill gaps in staffing numbers is totally unacceptable as these people are neither trained nor employed on the basis to work with people on probation.”

Recent inspections by the probation watchdog have uncovered serious problems in approved premises.

It raised raised “serious safeguarding concerns” at Weston AP in Weymouth, Dorset, because staff were not completing checks on residents at higher risk of overdose, key processes to tackle suicide and self-harm were not being followed, and there was faulty CCTV.

A MoJ spokesperson confirmed that the probation service continues to use security guards at the last minute to fill staffing gaps.

They said: “While a handful of premises are temporarily closed, we have increased the total number of beds available in approved premises so we can accommodate more of the highest risk offenders and keep the public safe.

“Approved premises is just one way in which we manage offenders in the community. We have invested a record £700m into probation and community services so we can ramp up tough supervisions on offenders released from custody, including punitive restrictions on their movements and round-the-clock monitoring through tags.”