Was this the ACAS helpline Puffins? It's a great resource and everything, but please don't rely on them for anything as complicated as this. There are a lot of complicated, interwoven issues here and it doesn't sound to me (ex employment lawyer) that they've fully appreciated them all.
There may be issues of disability law and reasonable adjustments. If you are disabled (and you might be within the meaning of the law, you'd have to find out) they have to make adjustments to try and allow you to stay in your job. If that isn't possible, before they dismissed you they'd be expected to think more broadly about adjustments (for example, not saying that you want this to happen, but you've talked about not creating a junior job. It's true that they don't have to create a 'fake' job. But surely if they promoted someone into your management role it would leave their old job as a vacancy?)
Even leaving that aside, whether they can dismiss you for competence is quite complex and depends on things like how long you've been off and prognosis. Even very senior employment lawyers and HR Directors will be cautious about saying it's ok to dismiss someone after a workplace injury (which doesn't affect the law, but does affect the sympathy of the tribunal, which is a big issue in employment law). I wouldn't rely on a helpline (or occ health) to make that call.
There may be additional complications if you have PHI insurance through your work. If not, look into whether you have it through any other avenue (most commonly mortgage).
Finally, in terms of initial comments, yes, personal injury is a possibility. It sounds like they royally fucked up health and safety.
I've been out of the area a few years now, but I don't think it's as simple as putting up with it.
I hope you aren't in tooo much pain and that it is being sympathetically managed with enough medication. So sorry to hear what happened to you.