A police force has been fined £234,500 over the death of Thomas Orchard, a church caretaker with mental health problems who died after a heavy belt was placed across his face while officers were restraining him.

Devon and Cornwall police were strongly criticised by Orchard’s family, the sentencing judge and campaigners, who believe it is a landmark case.

The decision has prompted calls for more national oversight of the way in which police forces use specialist equipment such as the American-made belt at the centre of the Orchard case.

Devon and Cornwall continued to insist the use of the emergency response belt (ERB) had not directly led to Orchard’s death, and said it would have to fund the fine by recruiting fewer officers.

Four police officers – a sergeant and three constables – and two civilian detention officers who were involved in Orchard’s restraint will now face misconduct proceedings.

Orchard’s family expressed anger the the force had still not apologised to them. In a victim impact statement, they spoke of the pressure the case had put on them and their distress at how he had sometimes been depicted during the court process.

“It has been hard to hear Thomas defined as an ‘angry man’ when we know he would have been a frightened one; to hear his behaviour described as ‘violent’ at times when we know he was fighting for his life; to hear the effect of his detention compared to that of the capture of a ‘non-human animal’; and to hear that officers thought he was ‘sleeping’ or ‘compliant’ when we know he was probably unconscious or even dead,” they said.

“It’s been painful to witness how an organisation, which had a duty of care for Thomas, was so casual, disorganised and sloppy in their approach to health and safety. A piece of equipment – the ERB – was used in a criminally unsafe manner around his face and we often wonder how Thomas’s life – and our lives – would have been different had senior officers in charge of health and safety for the Devon and Cornwall police force done their job properly.

“We are not confident that failures have been recognised and genuine changes have been made. We fear that other safety issues may remain unidentified; that others may be at risk.”

The office of the chief constable of Devon and Cornwall admitted breaches under the Health and Safety at Work Act 1974 at Bristol crown court.

It is the first time a British police force has admitted to an offence in such circumstances and is seen as hugely significant by campaigners, who believe forces and officers almost always escape justice after preventable deaths in custody.

Orchard, 32, was arrested and taken to a police station in Exeter in October 2012 after a disturbance in the street. During his detention, officers placed the ERB across his face. Orchard had a cardiac arrest and died in hospital seven days later.

Devon and Cornwall police admitted breaching the act on the basis there were failings over issues such as how officers were trained. Following a trial of issue last month, the judge, Julian Lambert, concluded he could not be sure the method of restraint had contributed.

But the judge flagged up that the belt had been approved to be used as a hood without risk assessment or research.

In mitigation, the force said the belt had been used on people’s heads about 500 times before Orchard’s death without reports of injury.

The judge said: “I appreciate that there is a significant body of evidence that no one was, in fact, killed or very seriously injured because of the use of the belt as a spit or bite guard. It is, however, my assessment that it was only a matter of time before someone was going to be.”

The family’s solicitor, Helen Stone of Hickman & Rose, said: “This case is also significant because it has exposed the worryingly haphazard way the UK’s police forces obtain and use the specialist equipment they deploy on Britain’s streets.

“Currently there is no national oversight of the way this equipment is procured, tested and used. Each force is effectively able to make its own decisions – and its own deadly mistakes. This is deeply concerning.”

Deborah Coles, the executive director of the charity Inquest, said: “The sentence should be a wake-up call to the Home Office and all police forces, who are failing to ensure there is systemic consideration of safety when introducing new, varied and potentially unsafe equipment into custody settings.”

Speaking outside court, Shaun Sawyer, the chief constable of Devon and Cornwall police, said: “My thoughts remain with the family of Thomas Orchard, who have suffered immeasurably following Thomas’s death.

“Devon and Cornwall police is a very different organisation six-and-a-half years on from Thomas Orchard’s death in terms of the training delivered to staff, awareness of mental health crisis and our ability to identify and manage violent, vulnerable people coming into police contact.”