"If you see a Rook all by itself, it's a Crow: if you see lots of crows together, they're Rooks!"
Now this bird's head-shape looks good for Rook, but its bill is more crow-like. Also, it has no bare patch on its forehead - nor sign of a developing one. Ipso facto, I'm going for young Carrion Crow: a welcome visitor to the garden, albeit one that the Jays are terrified of!
We also have a Jackdaw visiting most days that has a considerably paler nape than all of his mates: I wonder if it's one of the eastern-type Jackdaws? I'll try and get a photo if it stops raining!