Perish the very thought that I should ever be accused of saying they were incompetent, but... "the largest pre-historic manmade structure in Europe" ?? Can that be right, and what do they mean?

Not the widest, or longest certainly. Nor the greatest volume I'd have thought. The highest? Maybe, but why not say so?

Could they mean "the greatest pre-historic manmade MOUND in Europe"? In which case, they've forgotten the recent considerable lengths their own organisation went to to show it was not just in Europe but in the whole world....

Big surprise,..."EH do Silbury an injustice"...