This is a member of the Crow family, a Rook (Corvus frugilegus ). They look quite similar to the other large crow, the Carrion Crow, but the easiest way to tell them apart is the white patch at the top of the beak. Carrion crows also nest in pairs and though they will gather in winter in large flocks, mostly they are seen singly.
Rooks on the other hand are very sociable, and nest in huge colonies called Rookeries, and will be found often in huge flocks.
A collection of Rooks is called a Building or a Parliament.
To see the rest of this coven of crows just follow the links...