I suspect that https://www.openstreetmap.org/way/384767796 is supposed to represent access to the lift, which I've never used.  It's a bit of an "artistic rendering" as the stairs don't spiral (see e.g. https://designstudioalexander.wordpress.com/2013/06/01/the-greenwich-foot-tunnel/ ).
I don't see a 300 degree turn, although as drawn in and out of the lift is about 170 (which makes sense when you think about it).  The steps take you through a bit over 2 full tuens (720 degrees) over course.