A faulty alarm system is putting hospital staff at risk from some of Scotland's most dangerous psychiatric patients, an insider has claimed.

The safety system at Carstairs^[1] state hospital was installed during a £90million rebuild just five years ago.

But a whistleblower claims the wireless personal alarms regularly go on the blink and back-up devices – a pager and a radio – are "useless" when nursing staff are under attack.

The source said there have been three assaults this year in which staff were left vulnerable when their calls for help went unanswered.

We revealed last month the maximum security hospital is in danger of turning into a powderkeg after six staff were attacked in one week this year.

Some staff and patients fear a return to the dark days of the 70s when murderers Thomas McCulloch and Robert Mone butchered a nurse, a patient and a police^[2] officer in an escape bid.

The personal attack buttons are meant to raise the alarm easily and let security staff locate the incident.

The source said: "This security system is virtually useless. Staff press their alarms and it fails to locate the person who is activating it or doesn't pick the activation up at all.

"So they gave the nursing staff back-up radios and pagers but they are useless as you can't restrain someone and free a hand to work a radio at the same time. Staff have zero confidence in it."

In March, the alarm system was activated three times by staff feeling threatened or under attack.

The source said: "Each time the alarm was pressed, nothing happened. One of the nurses was on the floor grappling with a patient, waiting for help that wasn't coming. Luckily, the injuries were minor."

In another incident, a dangerous patient attacked a member of staff whose alarm did not work. The whistleblower said: "What is the point in an alarm system that is not fit for purpose?

"One day it could have serious consequences for a nurse. This system was supposed to be the best. It's a total waste of money."

Last month, a whistleblower claimed staff shortages on some shifts and a lack of activities for patients were turning the Lanarkshire hospital into a time bomb.

During the attacks, a female nurse was so badly beaten that she looked like "she had been in a car crash".

A male nurse needed facial surgery after the same attack.

Carstairs is run by the State Hospitals Board for Scotland. It has 120 patients, including Gregor McGurk, who cut off his father's head in 1997 and kicked it around a car park.

A Carstairs spokeswoman said: "Safety of staff, patients and visitors is our highest priority. We have a sophisticated staff safety system in place to ensure this.

"As with any complex technical system, a fault is always a possibility.

"Because of this we do not rely on one single system – we have policies, procedures and equipment that work together to keep people safe.

"Our equipment and systems are under continuous review to make sure they are operational and effective.

"If any problems are identified, we act quickly to notify staff, address the problem and, if necessary, change the way we work to keep people safe.

"There were three incidents in March during which part of the staff safety system malfunctioned.

"This was immediately identified and there was an effective response to each incident.

"The reason for the malfunction has been established and shared with staff and we are in the process of implementing a solution."