I am about to start a PhD in October. My intended study involves examining crown court files (including psychiatric reports)and court transcripts. I have contacted the Home office about the matter and they advised me that it may not be possible to access psychiatric reports. They also sent me a very complicated application form. From other sources I have heard that it is best to contact the CPS about court files. Also court transcripts are very expensive. Has anyone any experience in this field? Any advise or exchange would be useful.
Thanks.

you are in for an uphill task as this involves a lot of ethical stuff. Wishing you all the luck in the world.

all i can say is that this is definitely something you want to discuss with your supervisor BEFORE you get in contact with those institutions. the point is, in difficult cases like this, one wrong word in an e-mail or such can make obtaining access incredibly hard, whereas your supervisor should know what the pitfalls are.
as you haven't started your PhD yet, I wouldn't worry too much yet. Talk to your supervisor; he/she is there to advise you.