Elena, your situation is horrendous and your manager seems to be quite horrible. It might be a bit late in the day now, but one of the things you can do is keep a daily diary of your routines, what you have done, what you have tried to do and where you have been hampered, for whatever reason. You should also include conversations that you have had with your manager, especially when s/he has been unhelpful, ambiguos, or obtuse. The advice to get hold of your departmental policy to remind your employer of their obligations is also sound.
The fact that Unison is being completely unhelpful and inflexible comes as no surprise to me; I doubt that they would be much help anyway, they very rarely are.
It sounds like your manager has got in for you, so I think the best thing you can do is hang on as long as you can and in the meantime do whatever you can to get out of the place and start afresh somewhere new.
Things can change. I left a post 18 months ago because of a bullying manager and the move turned out disastrously. I actually wrote a long article about it for community care, but it wasn't good enough for publication, but it was cathartic anyway!
The team I joined was cliquey and in turmoil and took an instant dslike to me, for a variety of reasons, mainly to do with the flexible working hours I had agreed before starting the job. I got on very well with the manager though, but the team put in a complaint against him and he has been on the sick since, and work became a very lonely and hostile place. I felt (and was) completely unsupported and isolated,and it was all prety hellish.
Finally an acting manager turned up who had clearly been briefed about me, but we had a very frank and open discussion and agreed that we would start with an absoultely clean slate, and she made it clear to other team members that gossip would be not be tolerated. Not long after, a new service manager started who acknowledges the good work I do and as far as I know, knows nothing or little of my previous reputaion. Added to this, some difficult team members had moved on. The upshot is that my office is a much more pleasant environment. It's not exactly heaven, but it does illustrate that things can improve massively, in a short space of time.
My advice to move on holds though. I was recently offered another job with a different authority, which would have been a promotion, the reference from my current employer was good, because they told so me at the interview, once they received the reference from previous employer though, the offer was withdrawn, without any explanation whatsoever. If your current manager really is vindictive, he has the potential to hold a malign influence over your life for years to come. The chap who didn't like me gave me a good reference to get my current job, presumable because he wanted me out, and this could be the case with you.
Anyway, good luck and I hope it turns out well for you.