First of all I must apologise for the quality of this photo. This spider was found in my car in Coventry, wandering around at the top of my windscreen/headlining ... a bit of a shock whilst driving. I then parked up, caught it and placed on the road surface outside and took this photo. I would estimate the body length (rear of abdomen to eyes) to be 8-10mm. I have no idea how it got to be in my car, as I haven't moved any garden waste or old objects with my car; might there be more of them?
This is a missing sector orb weaver, probably Zygiella x-notata. These are very common spiders, often found on, around & in man made structures such as houses (especially window frames), cars, climbing frames, etc.