1.Well developed herb paris? Paris quadrifolia (cant quite see the shape of leaves)
No. The leaves are shaped more like a goosefoot or nettle, although the texture is unlike either of those (more smooth and shiny.)
2. looks like dog mercury/Mercurialis perennis
No. None of them are Dog's Mercury, which is a ubiquitous weed all over Sussex. Too big.
3. Looks like rose bay willow herb/Epilobium angustifolium
With yellow flowers??
I'm glad they're not easy, anyway!!