A major mental health unit for armed forces personnel was condemned as “wholly unsatisfactory and unsafe” by one of the most senior psychiatrists in the services, it has been revealed.

A 2015 report into the mental health unit at Tidworth in Wiltshire obtained by the Guardian found that targets set for the department were “unsustainable and dangerous” and that “the clinical workload expected of staff is unsustainable and is putting patients at risk”. Concerns about mental healthcare for thearmed forces have been raised for years, especially following the conflicts in Afghanistan and Iraq.

A whistleblower who worked at Tidworth until recently contacted the Guardian to hand over the report, which was written in October 2015.

In response, the Ministry of Defence said that significant reforms had been made since the report and pointed out that inspectors took the facility out of special measures six months ago. But the whistleblower said that the situation at Tidworth remained “appalling” and that soldiers were dropping out of the mental healthcare structures and “being lost to the system”.

Nia Griffith, the shadow defence secretary, said that the situation was unacceptable. “This report needs to be taken very seriously, and mustn’t be swept under the carpet,” she said. “The rhetoric seems to be there, but the reality is quite different, and that is worrying. The earlier that help and support can be provided, the less likely that it is to escalate into a crisis. It is high time that we had the appropriate mechanisms in place.”

The report into Department of Community Mental Health (DCMH) Tidworth noted a collapse in staff morale. “Burnout was evident in many staff members including anxiety, low mood, insomnia, withdrawal, apathy and a pervasive sense of helplessness and lack of control,” its author said.

“The utter fixation on clinical targets has led to a ‘sheep dip’ approach to meeting numbers, and some clinicians report desperate patient contact without clear purpose.”

The report was written by Surgeon Commander Rik Coetzee, head of psychiatry for the Royal Navy. It also made clear that the situation at Tidworth had become a serious ongoing problem, with “several attempts at reform and amelioration […] met with limited success or outright failure”.

A spokesperson for the MoD said: “The welfare of our brave armed forces personnel is of paramount importance and we regularly review our facilities to ensure they deliver effective healthcare. Over the last two years we have improved training, helped staff manage workloads, and allocated extra space for patients. As a result, inspectors took the facility at Tidworth out of special measures six months ago.”

According to the report, the clinic at Tidworth was not fit for purpose, with a “chronic shortage of clinical space”.

The report said there were “clinicians desperate to meet their clinical targets, but have no clinical space allocated ... [They] scour the administration office in the morning, hoping someone may call in sick or no longer need their room.”

The Tidworth garrison was recently overhauled as part of the MoD’s £8bn Project Allenby/Connaught infrastructure refurbishment. A spokesman for the MoD said that DCMH Tidworth had recently been allocated a new building, and was “due to occupy this space in the near future”. The whistleblower said that the situation was having serious consequences.

“In the armed forces, it’s hard to come forward, not least because of the career effects, so if at that point they are being treated like this, then it’s appalling,” said the whistleblower. “You don’t fix people operating like that. You actually just make them worse, because they lose faith in the system.”

Hundreds of soldiers are based at Tidworth, with the 1st Armoured Infantry Brigade and the 1st Artillery Brigade headquartered there. The whistleblower said that Tidworth’s role as the headquarters of the south-west region meant that the mental health facilities were crucial.

“People would be travelling for two hours and they would miss a call and arrive and be told that their appointment had been cancelled. People just drop out of the system at that point. They’d stop turning up, and that would be seen as a good thing because it freed things up.”