The NHS doctor told him, he didn't have ADHD, 3 private clinics told him he did
and your reply is 'The NHS is not fit for purpose' ?
The reason he was able to get a diagnosis from the NHS is because he is a BBC journalist, and is able to navigate any bureaucracy as part of his work day and get paid for it, and ultimately does not suffer from the disorder and thus doesn't really care how long it takes for him to get seen by the doctor.
The average person would be stuck in a kafkaesque maze of bureaucracy and months-long waiting lists before they get anywhere close to a diagnosis (which is even worse if you actually do have a disorder and is impeding your day-to-day life and/or work) - that's why these private clinics have business.