I'd be surprised to find that buzzards are taking pullets. I lived in Exmoor for years, with plentiful buzzards and lots of friends breeding chickens, and never heard of a buzzard taking one. A goshawk will take a hen, though, and it's easy to think you've seen a buzzard if you didn't realise you might be looking at a goshawk

I've not heard of buzzards eating snakes. They take carrion, and love rats. According to the RSPB website, they will eat earthworms if they can't find their favoured foods, but it doesn't mention them taking adders...
The most prevalent predator of snakes in the UK is surely the hedgehog?
And, according to something I read, if they have grazing ponies on your common, they'll kill snakes if they come across them
