aaj wrote:
Hi all

I'm a new gardner so please excuse my ignorance in all things
green...

The more gardening I do, the more ignorant I find I am! Like any
other worthwhile activity, so there's no shame.

[...]
Or, (as I suspect might be the answer) do I have to keep digging
and
turning the soil until I've removed all the roots.

thanks in advance

If you plan to use a herbicide, I'd be inclined to leave it all alone
for several weeks so the roots can send up some shoots. Poisoning
buried roots rather than active top growth isn't practical, and
wouldn't be healthy. Most of those 12" down won't make it to the
surface, but the rest probably will.

You need to let it all settle undisturbed before seeding or turfing
anyhow, so this sounds like nature's warning to take a well-earned
rest.

Turf won't provide a barrier against rooted weeds, though it'll stop
some of the ones coming from seed on the bare surface. If in no
hurry, I'd save the money and sow seed, which often gives you a
better lawn anyhow.

--
Mike.