You don’t say what size it is but it looks like hedgehog to me.

Pheasant is a possibility. Hedgehog is made up of chitin which is the black shell of beetles etc.

not hedgehog but my first thought was avian rather than mammalian. gull/rook/crow and as Owd suggests pheasant also a possibility.

any particular smell? I know that sounds disgusting but smell is often very diagnostic.

I had read that the smell might be usefull, so I squished it. Didn't seem to have any noticeable smell. It was smooth, like pate.
Don't think it's pheasant, we have pheasants in winter, their poo looks different.
Do owls defecate while flying? Neither this not last week's 'sample' was under a perch of any kind.
Weirdly fascinating stuff .... 🤔

Not mammalian then as all of those are described as being 'scented'.

No idea but found a site with a forum you can ask http://www.discoverwildlife.com/british-wildlife/how-identify-animal-droppings
It could be that the animal has a problem with its biliary system which can have that grey result. Please let us know if you find out!

yes owls do defecate as well as regurgitating a pellet of fur and bones.
I've checked my animal tracks and scat guide and it doesn't match any mammalian scat in that.

i'm inclined to think waterfowl such as geese but difficult to id.