Please get informed behind the scenes, you don’t have to want to leave your job to get armed with knowledge and insight about employers, disability and grievance processes.
I can feel how much you love and want to keep your job. Definitely keep this aim and use it to make it clear what your aims and also ethics are throughout this process.
But... do keep in mind that you cannot control the process. The law is completely and absolutely on your side. It really is. But, it’s not the law that will decide how the company will choose to behave. That, sadly, is up to them.
If they decide it’s in their interests to squash your complaint and make the problem disappear by telling you it doesn’t exist, then you may find it too upsetting to work there afterwards.
If they decide to stick by the manager and keep it in house by enabling his behaviour, then, again, you may find your situation has been spoilt by them.
However, if they can see that it’s in the company’s interests to distance themselves rapidly from any disability discrimination or inequality, then it can easily be dealt with so that you can keep your job and put this behind you.
This is why you need to armour up with some knuwledge now, and some reallly good phrases to put into emails etc with HR / the company management. You need to make it clear that it’s better and easier for them to deal with this fairly and by the law, and it would put them in an uncomfortable and difficult position to be seen to condone and agree with disabilist and discriminatory behaviour.
Basically, make it easy for them to do the right thing, and harder the do the wrong thing. Sadly that works waaay better than appealing to anyone’s morality or sense of wanting to do the right thing!
Applying the right kind of pressure now is important. Politely, with a smile, always explaining your commitment to the company and your desire to get back to working without this barrier. But making it clear the reality of the situation.
Please go get that legal advice and those great phrases you need to drop into your communications. Do it now, not later once they’ve already made up their minds (that was my mistake, I was too scared of annoying people and I paid for it later in spades - I had experienced legal advice telling me what I’m telling you and I ignored it!).