Wet and wading

Am late posting this tonight as I've been trying to find out what sort of bird it is. It looks like a heron, but it's all white. Perhaps an egret? But it's got a black beak, not a yellow one. Its feathers are fluffy, so perhaps it's a juvenile. And it's got this distinctive feather sticking out of the back of his head. It was wading in Kingsbridge estuary (ria) at low tide. Can anyone help me to identify it, please?

EDIT: New readers start here ... thanks to everyone who's identified this as a Little Egret. Am so excited, as I'd never seen one before!