Grey Squirrel – The destroyer. Squirrels are clever and can figure out how to lift tops off things etc. When this approach fails, they will chew through plastic and wire until they get where they want to be.
Snails – Just Grrr!
Small Tortoiseshell Butterfly – A thing of beauty and pollinator.
Common Frog – Devours slugs and snails and (ooops!) worms
Hoverflies – Sometimes mistaken for bees or wasps, these are harmless insects whose larvae have a voracious appetite for aphids. Hurray!
On the Fence:
Grass snakes are fascinating and one of the few reptiles native to the UK, but their diet consists of mostly amphibians.
Pheasants – Beautiful, but can be destructive in the garden, especially to snakes-head fritillaries (in my experience)