Bird of prey

I glanced out of the kitchen window this morning and saw a bird of prey perched on the back of the garden bench with its back to me, about 20 metres away.  Its head was facing sideways so I could just see an eye and the curve of its beak.  I rushed off to find my phone and got a series of very bad photos - I couldn't find my camera.  Its back was was grey with small white patches on its shoulders, and there was a tawny fringe of fluff just on the outline of its silhouette, where the wings folded against its front.   Looking at the bird book I think it was a sparrowhawk.