Kat is right mate, if your job is making you feel ill then you could have a legal claim. First of all can you bring someone with you for the meeting?,If you are not in the right frame of mind, you may not take it all in. The company sound they couldn't give a ****. If you cannot take anyone with you then seek advice for C.A.B as kath mentioned before hand and dont be shy in telling them ( dont lose your temper) what you intend to do.
Tell them' Unless the sitution improves, I will have to take the matter further, my doctor has offered to write on my behalf and though I love my job, my health has to come first."
A friend of mine just got a pay out of from coco cola, not long ago his wife lost a baby and he couldnot return to work for months. Coke done everything right as regards to letters, warnings and so on. I went to to meeting with him and said' your laywers will tell you that you have done most things right, but I know cases like this are won and lost on a minor technical points, have you been a 100% right?. The next day he was paid off.
Tribunials will always favour the employee so again without being cocky explain this in a soft tone.