Don't imagine getting to the top of the waiting list will solve your problems.
I have lengthy experience of NHS treatment of a non-life-threatening pyschological disorder (PTSD, which shares many external behaviours with ADD) and I'm sorry to say it was absolutely woeful, to the point that I was more distressed and dysfunctional afterwards!
My psychologist was far too young and too inexperienced to be helpful in any way. (Older and more experienced ones are assigned to the more serious cases during NHS triage assessment, such as victims of rape, war-crime and terrorism etc. This is understandable, but incredibly frustrating for the patient because your symptoms are the same even if the original cause was innocuous by comparison).
My "talking therapy"/CBT with this fresh out of college psych hopelessly out of her depth gave me depression so bad I couldn't get out of bed for days - not ideal when you're self-employed. Ofcourse, once she caused this additional problem she couldn't fix it, because psychologists are not medically qualified and cannot prescribe drugs.
More importantly, all NHS psychologists are restricted in the therapies they can employ to those which NICE have approved. Fine in theory until you realise some of the most effective mental health therapies - such as meditation and self-hypnosis, EFT, REBT and acupuncture - are not approved because they are not commercially viable and therefore don't warrant funding for the required clinical testing, not because they don't actually work.
Would you consider going private? If so, ask your GP for a referral to an ADD specialist (perhaps to both a psychologist and a psychiatrist). There are various books about ADD written by Daniel Amen which I read as part of my treatment and which I can recommend. If your attention span is shot, ask someone to read it for you and then tell you only the most relevant info.
Whether you're prescribed medication or psychological therapies, also think about getting help from a professional organiser. He or she will set up systems to help with the practical management of your condition. A friend of mine's daughter has just achieved 4 A stars in her A levels and credits not the school but the organiser who helped her get her notes and files in order every month!