Thank you for your response Keyur, you are correct, I am trying to use the sliding mesh method. I believe that a conformal mesh is being generated as you suspect but I am not sure why as the main enclosure and the disc enclosure are separate parts as you can see in the image below.
Then as I said in the original post, no mesh interface option appears in Fluent and no interfaces are made (or can be changed from interior) when I look in boundary conditions.
Also, I have already watched the video you added and can confirm my method is virtually identical.
If you have any further suggestions they would be greatly appreciated.