Do you have to pay council tax on any size land [arable / pasture land /
grazing / recreational / allotment-type land] if you are not using it
for
anything in particular (perhaps other than growing a few bits of food
for
private family consumption)?

You pay non-domestic rates on it.

Right. Thanks for that, that's a step closer to what I'm really looking for.
I've googled somewhat on that phrase (including the VOA site) and have not
found anything specific (loads of waffle about non-doms and tax though!).
I'm trying to get a rough idea as to what the total cost of ownership of
owning land might be. I'm wondering specifically how much council tax is
payable, say, per acre/hectare, etc?