It must have been nearly 20 years ago when I went there, organised by my instructor at Elstree for a small group of us to go there. Very interesting, we also visited the approach room. We were told to be very quiet at al times. The tower must have been very quiet that night because it was very relaxed in there, almost spa like.
A good thing to see, I remember the LTN chap that took us round (I think his name was Steve) saying that after the tower was built pilots complained it was too shiny and the concrete was a distraction. So they paid someone to Kango little chips off the entire structure to make it less reflective. I also remember the lift in the tower took 42 seconds to ascend.