I too had tinnitus for a long time and it all went away after chelation treatment against chronic mercury poisoning from amalgam fillings after being lucky that it was diagnosed (I had to actively search for a rare researcher/university clinic doctor specialist, nearly no chance with normal doctors). See my post history, I mention it a few times. I could write a few more pages about it all but in this format I'll leave it at that, people with the problem can decide for themselves if this is relevant for them. I was reluctant to post because I know a lot - most? - people don't take low-dose heavy metal poisonings seriously at all. I had people wanting to buy an espresso machine off of me despite me having revealed that I planned to scrap it because the water coming out of it had twice the official limit for lead in it (and the medical limit is zero so any lead would have been bad). Because "how bad can it be, such a tiny amount sure does not matter".
OP is from Scotland and I though it might be relevant because it seems they use that stuff according to this very recent document: https://www.gov.scot/publications/amalgam-dental-fillings-ac...
By the way, my tinnitus went away within year one of chelation treatment. However, after almost a decade (of continued occasional chelation because it still helped) I had a lot of activity all of sudden for a few weeks around both ears. For the last decade I had shifting activity patterns in various areas, so that wasn't a surprise, I had expected something like that since that was a major impacted area. For weeks I could not listen to music and definitely not use a headset. Something was going on there and it wanted quiet.. Anyway, long story short - I can now hear much better than a decade ago! I first noticed because I've had the exact same MP3 player with the exact same songs for well over a decade, and the same in-ear headset for just as long. Suddenly I had to turn the (numerically adjusted) volume much farther down, into regions where previously I could not hear a thing apart from "music plays". Now I have to play everything on about 10-20% less volume than before, and it all happened exactly after those weeks of activity (where I even had to go to a doctor to get the ears cleaned, there was way more ear wax than usual during that time).
Chronic heavy metal toxicity is a subject rife with quackery and pseudoscience, especially when people start talking about chronic poisoning undetectable by conventional medicine. It's best to be careful whose story you believe. It's a hot button issue for me as a person "on the spectrum" because ill-informed parents subject their kids to Cutler protocol and other fringe chelation therapies under the belief that they're "curing" their kids of autism, and causing more health problems than they fix (chelators are themselves pretty toxic!)
Here are some resources about metal toxicity pseudoscience:
http://www.thinkingautismguide.com/2010/07/autism-and-biomed... (section "The Cutler Protocol")
Also, my jaw was in a bad state - a needle meant for mucosa injection went right deep in - in exactly all the places where I had had amalgam fillings. Nothing ever showed up in x-ray - which is normal, bone damage shows up in x-ray only when it's extreme (although a needle easily penetrating bone already is quite extreme). The doctor injected DMPS (chelator), the jaw healed.
Also, an double-size right-side thyroid with a nodule, stable for 2.5 decades, within half a year completely disappeared to the great amazement of my endocrinologist who had recommended surgery. There was lots of activity in the tissue around that area in my neck starting after I got chelation.
Warts on my feet, getting more and more numerous over the decades, completely gone.
Winter depression, psoriasis, colds (before diagnosis lasting the entire winter, getting longer and longer), eye issues, comprehension issues, digestion was bad and now is wonderful, - a long list of stuff JUST GONE NOW.
Look in a mirror for who is the quack, not to mention that with your accusation and remote diagnosis you are being quite an asshole.
The doctor I'm seeing is a researcher at a university clinic and always talks in "studies" and is very careful, never making any promises, always cautious with recommendations, preferring to do as little as possible. When I went there he said I must have something else, the levels of mercury found justify chelation treatment but are not high enough to explain all my problems. He never found anything else and improvement was far exceeding expectations. With chronic poisoning most of the stuff is hidden and comes out slowly, so yes, lab measurements usually cannot show it, I was "lucky" I had such highly elevated values. The doctor also makes no money - the university clinic charges a tiny bit (Germany, not US, it's next to nothing because there is nothing expensive, no medical imaging, just a few cheap lab tests, the chelators, DMPS and DMSA, some minor additions, are extra but inexpensive).