Given that I only saw my first ravens this year, I'm a bit hesitant to call these, especially as there were so many - over twenty in total. The numbers suggest they're more likely to be rooks, but their behaviour was not rook-like, and while it was difficult to judge size, the impression I had was too large to be rooks. (I thought "buzzard" initially when I saw the first bird, then they just kept coming ... ) They do seem to have the diamond tail shape of ravens.
I have a lot more photos, but none of them is any more helpful, I don't think.
LesleyL said: I've always had an image of them as fairly solitary birds.
So have I. When I first saw your photo I thought they must be rooks ...... but those tails were rather diamond-shaped. I'm delighted you had such a fantastic sighting!