I went in and in the top last week. The building has been stripped but going on the top and also looking at the partially demolished parts was fun. They've demolished two of the four wings of the main building. It's going to take them weeks to finish the demolition. There's a staircase in the centre and one at the end of each wing. There's some cameras on the perimeter but I found a route that avoided them. Tip: take a look behind the green gas service building next to the traffic lights. I don't think security were on site. There's normally a car parked outside the security hut, but my route is hardly visible from their hut anyway. They don't seem to do any demolition work on weekends.