Corvid Silhouettes - Rook or Raven?

I saw these earlier today, but the light was poor, and the photos are not very good.  There are an awful lot of rooks around, and we don't have carrion crows, so normally I'd accept any large, all-black bird as a rook, but these seemed too big.  There were six of them, and when I caught sight of the first one, my first thought was "buzzard".  I quickly realised it wasn't, although the circling and gliding flight was very reminiscent of buzzard.