Black storks in West Sussex?

I've just been walking my dog along a river. I'm not far from Pulborough brooks (5 min drive) so that's why i've come here to see if anyone knows if there are black storks in the area? I crossed over a bridge and a huge black bird took off beneath me. It was quite heron like but completely black. It had been paddling about in the stream. It wasn't a cormorant, seemed a lot bigger. It landed a bit further down the stream and i could see it looking at me, but it had its head tucked so i couldn't see its bill. Tried to sneak back along the path and could hear it walking around in the stream, but then another dog walker came up behind me so I decided to continue with my walk. A black stork is the only thing i could think of, is there anything else it could have been? About the same size, if a little bigger than a heron, long legs and a bit of an effort to take off.