NICE guideline NG87 sets out how attention deficit hyperactivity disorder should be recognised, assessed and managed in the UK. It is the standard NHS and private clinicians alike are expected to work to, and it is worth understanding before you book any assessment.
In practice, NG87 means a diagnosis should rest on a full clinical interview, a developmental and family history, information from someone who knows you well where possible, and the ruling out of other explanations. It is not a checklist exercise, and it is not something that can be done well in twenty minutes.
A private assessment that follows NG87 carries the same clinical weight as an NHS one. That is also what makes shared care with your GP possible, though shared care always remains at your GP's sole discretion. If shared care matters to you, speak to your GP before booking.
If you want the detail, the full guideline is published openly by NICE.
