Greg,
Mis-read the original post, sorry.
There is one interview at stage 2 - Hr only interview, then one interview at stage 3, HR + ATCO interview. Don't know what it was like for anyone else, but my stage3 was HR guy first, then ATCO with the technical Q's and pickups on a couple of my HR answers.
One tip for the 3rd stage interview, just in case. Try and remember as much as you can about what you were shown at Edinburgh. At my stage3 I mentioned I'd visited Birmingham, great until you consider the interviewing ATCO was a BHX watch manager
Fortunately I had an answer to 'tell me something specific about Birminham's airspace then'.
Stu