The charity worker had spent years feeling guilty for "being lazy", and after quitting university, and later his full-time job, he had told himself he was simply a failure.

"I felt like there was something wrong with me," he said. "I genuinely felt like a piece of me was missing, which is this part that everyone else seems to have to be able to get on with what they need to do."

Now he finally had an answer - he had mixed ADHD, leaning on the inattentive side.

But his journey to a diagnosis didn't take place within the promises of the NHS constitution, instead, it was funded by a credit card.

The 28-year-old had been waiting for more than a year when he took out the 0%-interest finance to fund a private diagnosis, after being told he could spend a further two years on NHS waiting lists.

And his experience is not unique.

New analysis estimates 800,000 people with undiagnosed ADHD may be left waiting more than a year for a diagnosis.

Five times more likely to attempt suicide

The NHS constitution states people have a right to NHS support for ADHD within 18 weeks of a GP referral. But new data suggests almost a million people are exceeding this target.

Increased public awareness of ADHD, workforce pressures, a backlog from the pandemic, and historic underfunding of mental health services means hundreds of thousands are at risk as they wait.

A report from CHS Healthcare - a longstanding partner of the NHS - alongside neurodivergent charities, The Brain Charity and The Donaldson Trust found people living with ADHD are five times more likely to attempt suicide (14.0% compared to 2.7%), making the need for assessment and support vital.

ADHD assessment data is not routinely published by the NHS and a lack of transparency and publicly available data around ADHD referrals means that the crisis can go unrecognised with no clear accountability. Because of this, patient advocacy groups have even suggested that of the 2.6 million people who have ADHD in the UK, two million are left undiagnosed.

The organisations are calling for dramatic reform to improve access to ADHD assessments, treatment and support.

A 'clever but lazy child'

Combined ADHD is characterised by both hyperactivity and impulsivity as well as inattention. For Jay, this meant for years he was labelled a "clever but lazy child".

"I was never bouncing off the walls, or being loudly disruptive, but I just didn't pay attention unless I was interested in the subject," he said.

Within the confines of education, he received enough support. But when he started university, he began to run into difficulties.

He said: "I was always skirting the line of, 'will I / won't I pass'. I managed to scrape through at the end after three months of really aggressive, hyperfocused revision.

"And then I did a Master's degree, but I failed it because I couldn't organise myself well enough to write a 12,000-word dissertation without support."

Life, he said, began to "fall apart" during the pandemic, away from the structures of his workplace: "I felt very anxious and isolated all the time."

A 'soul destroying' wait - and a clean slate

After doing some of his own research, Jay said the "penny slowly dropped" - it wasn't a personal failure, but a medical problem.

He spoke to his GP and began a pathway to diagnosis, but after being told it could be November 2024 before he was seen, he chose to pay and go private.

Choosing a cheaper private option - still at a cost of £380 per appointment, with medication costs £80 a month - meant waiting three more months.

"It was soul-destroying because there was no timeline on how long it was going to take," he said.

But during a video call at the start of the year, Jay finally got the answer he needed.

"It was an immediate release of all that guilt I had been holding onto about failing my masters and walking out of a well-paid job because I couldn't cope with it anymore.

"I felt so much relief to know, actually I couldn't have done it any differently. I had done the best with what I had."

For Jay, his diagnosis represents a clean slate and the opportunity to access support and medication.

And while the exact cause of ADHD is unknown, the condition has been shown to run in families.

Jay said: "My mum felt almost like it was a personal failure of hers for me to have an undiagnosed disability, and it took a long time for her to come round to the idea. And she didn't really accept it until after I got my diagnosis.

"But now she is seeking one for herself."

Damage inflicted 'enormous' as people left in limbo

Eleanor Norman, a former mental health nurse and client partner at CHS Healthcare, said the damage being inflicted on people's lives as they are left in limbo is "enormous".

"Timely access to assessment is vital," she said,

"A long wait to access these services is incredibly challenging, and in some cases can have a negative impact on people's health, work, and relationships."

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But NHS services and professionals are simply unable to meet spiralling demand, the report found.

Ms Norman added: "We need a collaborative approach that sees the NHS, third sector, and private companies working together to create assessment pathways that tackles the backlog and speeds up access to these vital services."