We're not sure what kind of plant this is. We've given the reference books a scouring and have not come up with a convincing answer. It looks very much like briars from a bramble or blackberry but then it looks like wild rose briars too, so who knows.
The thicket is about twelve feet thick, ten feet high and fifty yards long and incredibly dense and interwoven with other creepers and plants, it's growing close to the tidal river so maybe the influence of a little salt in the air has changed the colour of the stems and stalks.
It would certainly make an impenetrable hedge or natural wall so perhaps I'd better take a few cuttings and sell them to President Trump.
I wonder how quickly it grows.