Should I secretly record a meeting to prove I'm being discriminated against? I'm a PhD student at a university in the UK. The head and director of graduate studies at my department are trying to get me removed from the department.

Almost all of this is going on over my head, but my supervisor has told me about a number of meetings and emails that have gone on about this topic.

On the basis of what my supervisor tells me, along with my own previous interactions with the head of department, I feel quite sure that what they are doing is discriminatory against me due to a disability that I have.

However, since I am not included in any of the emails etc. about this, I have almost no evidence. This makes it very difficult to defend myself against what they are doing and saying.

While my supervisor is on my side and doesn't want me to be kicked out, he has a very poor understanding of disability issues and discrimination. His number one priority, of course, is protecting himself - ultimately it looks really bad for him to have a student that the head of department warned him would be trouble and ends up getting kicked out.

So he will tell me about these things in person, but not by email - if I ask him anything by email, he asks me to come to his office to discuss it. 

Should I secretly record a meeting with him where I bring this up so that if it comes down to it, I have some evidence that the action is discriminatory?
No.

Such action should be the very, very last resort, and only undertaken if you have taken legal advice on whether it is advisable to do so.

As a UK student, you should have support available to you from the Student Union, which will almost certainly include disability representation.

The Student Union will be able to advise you on how to proceed on this matter, and possible provide you with a third party representative to join you at any meetings you have.

Also, you mention emails that exist 'about you.'  You are within your rights to request these to see what they say by making a freedom of information request.  Again, seek advice first before undertaking this action.