A quarter of all crimes are committed by people with mental health problems, the first study of its kind has revealed amid a sharp decline in NHS care for the mentally ill.

The findings by six criminal justice and health watchdogs show that mental ill-health played a part in 24 per cent of offences, equivalent to more than 1.3 million crimes, ranging from thefts and assaults to serious sexual violence, murder and terrorism.

It is the first time the six inspectorates, including police, prison and probation, have quantified the crime attributed to mental ill-health, although police chiefs have previously warned that up to 30 per cent of officers’ time is taken up dealing with mentally ill offenders or members of the public.

The report, published on Wednesday, comes after it emerged that Emad al-Swealmeen, 32, who blew himself up outside a maternity hospital in Liverpool on Remembrance Sunday, had a history of mental health problems and was once sectioned for brandishing a knife near Liverpool city centre.

Up to seven in 10 people referred to the Prevent counter-terrorism programme may suffer from mental ill-health or other vulnerabilities that could leave them prone to falling for propaganda from violent extremists, according to police.

Justice system ‘is failing the mentally ill’

In a damning 117-page report, the watchdogs said the criminal justice system was failing people with such acute or severe mental health problems at every stage.

When they should be treated in hospital, suspects or offenders in need of mental health treatment were instead being locked up in custody or held in prison for up to a year longer than they should be because no secure mental health beds were available for them.

The inspectors warned that the consequence could be increasing crime as offenders suffering from mental ill-health were more likely to reoffend if not properly treated.

The report said official data showed the number of mental health beds in England had fallen by 73 per cent since 1987-88, from 67,000 to 18,400. By comparison, the number of general and acute hospital beds had fallen by 44 per cent from 181,000 to 101,000.