A lot going on –
The snail has been tentatively identified as possibly being of the brown-lipped variety.The insect appears likely to be a member of the Auchenorrhyncha group, either a froghopper or leafhopper. The tree is a young aspen with leaves suffering from the fungal disease, leaf spot.
Pictures taken July 31.
Thanks for ID help to @missattitude198, @BC_Norfolk and @Lytchettbirder who all got in touch via @wildlife_uk.