Police and ambulance crews were called to a serious disturbance at Britain’s most high-profile secure mental health hospital - months after staff raised concerns about under-manned wards, it has emerged.

Officers from Thames Valley Police’s public order response team attended Broadmoor Hospital in Berkshire after violence flared in Epsom Ward, the police service confirmed to HSJ.

South Central Ambulance Service Trust confirmed two people were treated by its crews at the scene of the incident and that it had sent a “hazardous area response” team to the hospital. West London Mental Health Trust, which runs Broadmoor, confirmed that the ward had sustained damaged from the incident, which took place in July last year.

A source with knowledge of the incident told HSJ it was triggered by patients in Epsom Ward having been regularly locked in their rooms for 20 hours a day, and that this seclusion was enforced because of understaffing. This had been ongoing for a year, the source said.

The trust denies there was a shortage of staff, and that the incident was linked to a staff shortage.

The 12-bed ward houses patients with complex and challenging personality disorders, some of whom can be dangerous.

The incident is understood to have been ranked a “silver command” incident, the second most serious category at Broadmoor which involves calling in outside emergency bodies.

West London Mental Health Trust confirmed that patients had taken over the nurses’ office on the unit during the July incident but refused to confirm or deny reports from the well-placed source that they had accessed the medical notes of other patients.

The trust had been forced to transfer patients out of the hospital because of the alleged breach of patient confidentiality, the source told HSJ. The trust refused to confirm or deny this.

A spokeswoman for the trust said it had “fully investigated the incident” but refused to release the report it produced as a result of its probe. Its release could compromise “the maintenance of security and good order” and “health and safety”, she added.

The Care Quality Commission confirmed that concerns about “inadequate levels of staffing” on Epsom ward had been raised by staff at the hospital during a visit by Mental Health Act commissioners in April 2013, three months before the incident.

And a CQC inspection just weeks before the incident found “a few examples where the use of seclusion for nursing people might not have fully complied with the Mental Health Act code of practice”.

“Our findings highlighted that seclusion might have been used pre-emptively as a way of managing the ward environment rather than as a response to the violent or disturbed behaviour of individuals,” the official investigation report states.

The inspectorate would not reveal whether inspectors visited Epsom ward but concluded that the hospital met all six of the commission’s standards, including in relation to staffing.

The CQC report stated: “The majority of staff we spoke with told us they felt there were enough staff on duty at all times and additional staff could be provided, if required.”

The trust refused to confirm whether patients had been regularly detained for 20 hours a day.

“[We] may use seclusion to keep others and patients safe,” the spokeswoman said. “We constantly review its use in order to ensure we provide the least restrictive therapeutic regime possible”.

The trust investigation found no link between the events and staffing levels, it said, bit it would not put a figure on the cost of repairs to the ward, she added. “To provide specific details about the costs of repairs within the secure perimeter would indicate the nature and scale of any damage which had occurred.”