I have just moved this from chat - hoping to get some more advice : Update, have joined a union today 
Have name changed for this and put it here, hoping to get some help sad. I really am unhappy at work - not because of the job but because my boss is just awful. She is putting me under so much pressure and I, quite literally have no-one above her to turn to. I know that sounds silly, but it is true - she is the top, and has no senior. There is a board of trustees, but I have attempted to talk to the chair before who simply agrees with my boss and is no help. I don;t belong to a union, and, although I know a lot of people will disagree, have not found unions very helpful in the past. I spoke to ACAS recently and they weren't terribly helpful either! the latest 'capability' she has put me on (she is always doing this, depsite that fact that I know i fulfill my job description (and more) to the last dot,) states i am not allowed to talk to anyone about how I am feeling, except her and that she will sack me on the 24th January if I don't reach her standards. She is a control freak, and I am so unhappy. Do I leave? I've been in this post for 18 months and apart from this, do enjoy my job. All the other staff,(who I manage) can't stand her either but they don;t have to deal with her in this way. Please advise me!!