Lack of awareness of the behavioural disorder has meant many people found it difficult to hold down jobs. But proper diagnosis and support are allowing more employees to make the most of their talents.

As an employee, I wasn’t very good because I was inconsistent,” says Jannine Harris, 44, from Northampton. “I’m brilliant, and then I’m rubbish. And that’s obviously frustrating for an employer to contend with because they don’t know which Jannine they are going to get.”

Harris says she lost, or left, more than 40 jobs before she settled in her current role at Billing Brook school as a special needs teacher. “I’ve been dismissed from so many jobs,” she says. “That was the cycle of things. The only time I managed to hold down a long-term job, before my current one, was when I worked for myself for six years, but I only managed 13 months in a job prior to that.”

Harris was unaware that her inconsistency and flightiness was due to undiagnosed attention deficit hyperactivity disorder (ADHD), a neurodevelopmental disorder that describes a group of behavioural symptoms including inattentiveness, hyperactivity and impulsivity. The problems that Harris experienced at work are shared by many who have the condition. A new report into the socioeconomic impact of ADHD, conducted by Demos, a cross-party thinktank, found that it can be associated with lack of career planning, poor workplace productivity and increased job instability. The report also found that the likelihood of being a recipient of welfare benefits was 15% greater among individuals diagnosed with the condition.

The findings in Demos’s report correlate with my own experiences at work. I was diagnosed with ADHD in the early 1990s, when I was six years old. Educators were not aware of the condition back then, and I was expelled from every school I attended, finally leaving school altogether aged 14. The lack of qualifications that result from such an early withdrawal from education restricted my career choices to relatively mundane jobs.

Many people can tolerate the monotony of doing the same task over and over again in low-paid roles but, for me, it was intolerable. For example, in 2010 I had a gardening job with Oldham council. One of my daily duties was running a dutch hoe through flower beds to excavate the horsetail weeds that had taken root there; it was like a never-ending game of whack-a-mole. So rather than stick at this task, I felt it would be far more entertaining to twirl my hoe around like a ninja weapon and fill the rest of my time by winding up my colleagues. The council was quite tolerant and did everything it could to accommodate me despite my bad behaviour – including giving me time off to get treatment.

I’m brilliant, and then I’m rubbish. And that’s obviously frustrating for an employer to contend with

I was diagnosed with ADHD at a young age, but many adults struggle for years without knowing why their relationships and jobs keep breaking down.

Dan Maudsley, 38, who works as a senior broadcast journalist for BBC Radio 5 Live, says his life was at a “crisis point” before he was diagnosed three years ago. “In a sense, working on news summaries is quite good for ADHD, because the deadlines are short and it keeps you on track.” But Maudsley would be writing the summaries down to the wire and it was beginning to grate on his colleagues. “I think that if I hadn’t been diagnosed I would have been out of work and divorced, because deterioration at work leads to deterioration at home,” he says.

Since his diagnosis, Maudsley takes medication to control his condition and has devised other strategies to make sure he functions better at work, such as keeping a timer on his desk to help him visualise time.

But for John, a former housing options officer from Leeds, it took being sacked from his job and a suicide attempt before he received a diagnosis of ADHD. “I always knew I was different somehow, but I didn’t know I had the condition,” he says . “So I spent the last 30 years thinking I was inferior, because I found it harder to do things that most typically minded people take for granted.”

John says he was good at dealing with clients but struggled to keep appointments or turn up on time, and was generally disorganised. Since starting on medication, however, he is doing much better and plans to set up a not-for-profit organisation for housing the homeless.

Absenteeism is an issue for a lot of those with ADHD. When I meet Simon, 45, in Canary Wharf, east London, he tells me that things started going wrong when he changed roles. “I got offered a job that I thought was a great next step, but it didn’t quite work out. It took all the nice things about the old job and left all the dross. I had been able to cope with that as a small percentage but not 100%,” he says. Simon works as a business analyst for a prestigious financial company and says that when he started, as a temp, he had impressed his managers and was given more free reign as a result. “I was given space and other interesting things to do,” he says. “I’ve done well any time I had a management structure that allows that licence. The flip side is that when I have a management structure that is much more constraining, it goes the other way. I start switching off and become disengaged.”

Simon ended up taking six weeks off due to the stress caused by the change in roles and is currently working half days. After doing some of his own research, he thought he might have ADHD. He was formally diagnosed with the condition two weeks ago.

With undiagnosed ADHD presenting a significant cost to the country, what can employers do to ensure their employees don’t deteriorate at work? For Michelle Beckett, CEO and founder of ADHD Action – a charity that is lobbying the government to create provision for those with the condition – the key is in raising awareness. “I think people with ADHD do have a lot of strengths if they are supported properly by employers,” she says. “You don’t need a lot of extra resources to manage an employee with ADHD.” She believes that small businesses could benefit from the type of brain that someone with ADHD can bring.

Simone Vibert, a researcher at Demos and author of the report into the socioeconomic impact of ADHD, agrees with Beckett: “People with ADHD who have received a diagnosis and support can be immensely valuable to employers One phenomenon common among people with ADHD is ‘hyperfocusing’ – the tendency to focus on certain passions, interests or work very intensely – which could prove very useful in a work scenario.” She adds that employers should work with individuals with ADHD to identify their best support strategy. “ADHD affects people in very different ways [and] can affect the same individual differently from day to day. A task might seem easy one day but, at a later time, it might feel much more difficult.”

I spent the last 30 years thinking I was inferior, because I found it harder to do things that most people take for granted

She also recommends that employers and Department for Work and Pensions staff direct staff with ADHD to Access to Work – a publicly funded employment support programme that provides grants to those with disabilities. Vibert says: “The scheme can be used by people with ADHD to help pay for support such as ADHD coaching, which helps them to develop strategies to manage their condition and succeed in life, including in employment.”

ADHD is a highly treatable condition and if those who have it receive the right support, their lives can dramatically improve. For Maudsley, the most important thing an employer can do is “listen and have that conversation. It’s an ongoing conversation; there will always need to be adjustments throughout my career and it’s not always clear what they will be.”

Harris is similarly thriving in a working environment where she is supported by her employer, and works with a number of students who have ADHD. She is also involved in training and assisting teachers of inattentive or hyperactive students. “I teach literacy and it’s a perfect subject for igniting excitement and channelling energy. This makes me feel useful and valued.” She also feels that the school regards her ADHD as an asset. “No one expects me to run a standard, quiet classroom,” she says. “I am allowed to be me, with all my exuberance.”