The people responsible for the grounds of the apartment/ flat complex where I live were heavily pruning/ trimming the ivy/ plants around the base of the building today, which must have disturbed the spiders, because a large black white tail (? I think) spider just walked in through my window (I almost never get spiders in my flat). I put a cup over it to stop it moving, then grabbed a glass measuring jar to squash it with, but when I lifted up the cup it got away from me, and disappeared behind the back side of my computer desk. I pulled the desk back, but haven't been able to find it. So it's in the flat somewhere. 
Pics of white tailed spider
Pics of white tailed spider