Well advanced British \"Town\" predating Romans?

[Carus Andiae]

First I would like to know how the archaeologists know if there was olive oil used.

Not sure, but I think I'm right in saying that there were certain types of amphorae associated with different products (wine, oil, garum etc) and that some have been found stamped with the contents. Finding remains of those amidst the pre-Roman layer seems a possibility. Would be interesting to know, though.

But it does seem a fairly typical (over?)dramatised media report of a 'revelation' that isn't really news at all - though to be fair it might come as a shock to Joe Public (rather than people who study the period, which to a greater or lesser extent presumably covers most people in RAT), and I must admit a gridded town is a bit of a surprise for me.