Half of prisoners in London are believed to have undiagnosed attention deficit hyperactivity disorder (ADHD), according to concerning research published today. 

The figure, which experts say could help lead to a fairer justice system, is around 10 times higher than its prevalence of 5 per cent in the general population. 

The researchers found that half of prisoners arrested and detained in London may have undiagnosed ADHD, whilst one in 20 may have autism. 

Research has consistently found that people with these neurodevelopmental disorders are overrepresented within prison populations, with a growing body of research highlighting the link. 

Now, researchers at Cambridge University say that screening for ADHD and other neurodivergent disorders could help inform legal decision making, uncovering the potential reason for arrest and ultimately leading to fairer outcomes. 

Dr Tanya Procyshyn, a research associate at the Autism Research Centre, and study lead, said: 'To ensure fair treatment in the criminal justice system, we need to understand how neurodivergence affects interactions with the law.

'This can help avoid unnecessary criminalisation of misunderstood behaviour and ensure that potentially vulnerable individuals are able to access appropriate support.' 

They claim that routine examination of every new prisoner could help officers understand why crimes were committed, reduce violent incidents behind bars and help sufferers avoid committing further crimes by helping them manage the disorder. 

In the study, published in the journal Criminal Behaviour and Mental Health, Dr Procyshyn worked alongside senior detectives from the Metropolitan Police Service to offered prisoners voluntary screening for ADHD and autism. 

Over an eight week period, 303 eligible prisoner detained at one of six custody centers across the capital consented to screening. 

ADHD traits were assessed using a modified version of the adult ADHD Self-report Scale and carried out by a healthcare professional, detention office or arresting police officer. 

ADHD is defined as a persistent pattern of inattention and/or hyperactivity-impulsivity that has a direct negative impact on academic, occupational, or social functioning.

As suspected, eight per cent of arrested individuals had an existing ADHD diagnosis, slightly higher the prevalence of ADHD in the general population, which is around five per cent. 

But most interestingly, an additional 50 per cent scored at or above the threshold for possible undiagnosed ADHD.

This included 33 prisoners whose scores suggested a very high number of ADHD traits—which can cause someone to become very impulsive.

Nine prisoners had an existing autism diagnosis, which again is slightly higher than the prevalence of autism in the general adult population which sits around 3 per cent. 

An additional 5.4 per cent scored at or above the threshold for undiagnosed autism —a neurodevelopmental condition which exists on a spectrum, meaning that some will be able to lead fully functional lives with no additional help whilst others may need full-time assistance. 

According to police records, 60 per cent of those who tested positive for ADHD, or had an existing diagnosis,  were arrested for drug offences. 

Previous research has suggests that screening could significantly improve outcomes because ADHD is a highly treatable disorder. 

Therefore, a diagnosis could help reduce reoffending rates, with a significant number of neurodivergent people feeling the need to self-medicate with illegal substances. 

Several studies have also found that people with ADHD are less likely to engage in criminal behaviour when taking medication. 

Dion Brown, a senior Detective from the Metropolitan Police Service, added: 'Screening for ADHD and autism at the first point of contact with law enforcement benefits both the criminal justice system and the individuals involved.

'Early identification helps officers interpret behaviours that might otherwise be misunderstood and ensures appropriate support is provided. 

'This approach creates opportunities to divert vulnerable individuals away from the criminal justice process and towards the help they may need.' 

The report also warns that the failure to highlight prisoners with the attention deficit disorder as early as possible can result in  number of serious issues, one of which being violence behind bars. 

This is because being locked up in small, confined spaces can be very distressing for people with the disorder. 

Professor Sir Simon Baron-Cohen, Director of the Autism Research Centre, added: 'Screening for possible neurodivergence will allow more informed legal decision-making, taking into account cognitive and communicative differences.

'It can also help ensure defendants get access to legal protection and appropriate counsel. This could improve both the treatment and experiences of neurodivergent people in the criminal justice system and ultimately lead to fairer outcomes, including protection under the law, which is a basic human right.'

It comes as Wes Streeting ordered an independent review into soaring demand for mental health, ADHD and autism services after warning of an over diagnosis of the conditions, saying the issues needs to be looked at through a 'strictly clinical lens'.