Melanistic grey heron? (Norfolk UK)

Last June I watched as a nesting avocet mobbed a heron, and took a few photos.  This was North Norfolk in June 24.

At the time I was engrossed in the behaviour, and didn't really give a lot of thought to the bird being mobbed.  Now looking back at the photos I can see it's not the usual grey heron.

Not the best pictures, but can anyone please confirm the ID?