Hi I saw the plant in the photograph yesterday, at the edge of Radipole lake in Weymouth. From the flower it looks like a Solanum, and the only one I could find online was Solanum prinophylum, from south Australia. I could find no reference to it being found in this country, does anyone know if it is? Thanks. David.
Looks a bit like Solanum pyracanthum, the porcupine tomato or spiny nightshade, native to Madagascar. The spines are usually more orange in colour though, but maybe they don't show up too well on the photo.
It could be Solanum linnaeanum, which is native to Africa but naturalised in southern Europe (waste areas and maritime sands). I am used to seeing it in southern Spain, but maybe it has now spread to UK.