Please held identify very loud meowing bird

Hello,

This is on the Essex coast - at 7am a very loud bird made me look up, a song I'd never heard before and so incredibly loud I thought it was an escaped kookaburra... Then the song changed to what I can at best described as a cat-in-heat meow, still from the same bird. 

I barely had time to take this very bad picture, and can't stop thinking about this bird. I have no idea what it is, only that it was about a small pigeon size with a short tail. Looked like a fluffy ball. It was alone and both looked stressed and making the local pigeons and rooks clearly nervous. 

Does anyone have any idea?