The cache was found 8 miles off Great Yarmouth and is the most northerly point in the North Sea that Neanderthal tools have been discovered. It had been feared that the ice sheets that destroyed most pre-ice age Brit-ish landscapes had done the same to the land surfaces which existed where the North Sea is now.
But archaeologists now suspect that some Neanderthal landscapes have survived under the North Sea. What's more, they are now certain that hundreds or even thousands of square miles of post-ice age prehistoric landscapes do survive there. On land they have largely been destroyed or degraded by centuries of agriculture, later human settlement and natural erosion.
Unclear why a bunch of gravel was excavated and shipped anywhere. Do they mine the bottom for gravel? The article notes that fishermen have retrieved some stuff over the years, presumably due to their nets grabbing stuff off the bottom. Still, as I've argued before, the anoxic bottom of the world's oceans will eventually turn out to be bigger than any "lost civilization" imaginable.
UPDATE: Aha, according to this it was the result of dredging.