This one is a Lace Web spider, Amaurobius sp ., and probably Amaurobius similis.
Several species of lace web spiders are common around the outside of our homes and gardens. They make a characteristic lace-like web on fences, sheds, walls and among general clutter around the garden.
Males are prone to wander indoors when mature and looking for a mate. Bites have been reported when a spider has been trapped against the skin, but with little pain or lasting symptoms.
For less shocking and hopefully reassuring information on False Window spiders please see the following link: