Prison psychiatrists are feeling so frightened at work that many are finding it “impossible” to provide a basic level of care to inmates, according to the latest research to document the deteriorating conditions inside Britain’s jails.

Another instance of the ongoing crisis arrived as dozens of prisoners were evacuated from HMP Guys Marsh after an inmate torched his clothes on the building’s roof, triggering a “large fire”. Although no one was hurt it emerged that during the Dorset jail’s last inspection, investigators concluded it was in “crisis”, that managers and staff had “all but lost control” and violence was so endemic inmates lived in fear.

This follows other prison riots, including one at Winson Green prison in Birmingham last year.

Declining safety levels insde the penal system are underlined by a new survey that found assaults on psychiatrists, and that up to 30 healthcare appointments a day have been cancelled in some jails because there are not enough officers to escort staff between cells and clinics.

The research by the Royal College of Psychiatrists (RCP) – launched after concerns that members were no longer able to deliver adequate mental health services in prisons – reveals that staff feel physically intimidated and unsafe.

One respondent predicted a mass exodus of psychiatrists from the prison service, largely for safety reasons as the ratio of prison officers to inmates falls as low as two to 100 in some facilities.

Experts have long warned of high levels of mental illness in the prison population, with one estimate suggesting that about 21,000 people – approaching a quarter of the total prison population of 85,442 – have bipolar disorder, depression or personality disorders. Other studies show that around a quarter of women and 15% of men in prison reported psychotic episodes. The rate among the general public is about 4%.

One anonymous prison psychiatrist interviewed for the survey said: “It is important that there is wider public recognition of the impossibility of delivering adequate health care in many prisons at present and, given that serious mental disorders are common among prisoners, a failure to meet their needs may, in turn, exacerbate risks to the safety of the prisons.”

The survey interviewed a consultant psychiatrist in each of the RCP’s nine regions in England and Wales to provide a narrative assessment of the state of prison healthcare in their area.

The responses reveal working conditions that are close to intolerable, with one describing how colleagues “constantly swim against the tidal wave of overwhelming morbidity”. They continued: “Even those who are very experienced and efficient in their approach to prison psychiatry are beginning to crack under the pressure. In summary, the feedback is that prison is a really unpleasant place to work, with many I spoke to looking at ways to get out.”

A lack of prison staff also meant that psychiatrists reported problems getting access to unwell prisoners in their cells – at least four prison officers are needed to accompany a psychiatrist to visit an inmate. Another respondent said: “Several others have expressed concern about their safety when they have to go to a wing to see prisoners who cannot get to the clinic or refuse to come. A lack of information makes them feel exposed.”

One side-effect is that prisoners with mental health issues are being targeting by other inmates. As one respondent said: “There are worrying reports of prisoners, especially those with serious mental illness, being bullied, exploited and isolated, with little chance of them being supported or protected – of an increase in self-harming and assault.”

The psychiatrist continued: “Clinics are busier and more disorganised. Colleagues express concerns about assessing or managing high-risk patients with little information or time, and feeling unsupported and wary of criticism if there is a serious adverse outcome. Access to psychological interventions is limited or non-existent. Listener, chaplaincy and counselling services are at breaking point.”

The increasingly unsafe environment is also highlighted by the fact that some prisoners feel sufficiently emboldened to try to intimidate female psychiatrists with overt sexism. One respondent said: “In prisons for men there has been an upsurge in sexist behaviour. Young women in particular, as they walk to appointments in the prison, have been harassed by prisoners shouting in chorus in such terms as: ‘Get yer tits out’.”

They continued: “There is no surprise that this is unchecked because of the greater tensions, but it is hardly fostering a climate in which anyone feels particularly safe and included, or promoting rehabilitation.”

Another cited factor was the “churn” of private healthcare providers following the decision to contract services in prisons to external providers. One psychiatrist, who works in a prison housing more than 300 women, said healthcare provisions had been “impacted significantly” by moving from the NHS to a private provider. They said that there had been “several self-inflicted deaths” of prisoners identified as high risk.

Professor Pamela Taylor, chair of the RCP’s forensic faculty, urged justice secretary Liz Truss to either reduce prisoner numbers or create a better ratio of officers to prisoners. She said: “Psychiatrists and other mental health staff feel so vulnerable in the prison environment now that they cannot do even the most basic things for their patients. We must remember that, eventually, prisoners will return to the community outside.”