Kirstey,
You definitely need clearance to enter an ATZ. If the airfield is AFIS or A/G, strictly speaking you don't need permission to do anything (except on the ground if AFIS). But you would always be expected to ask first.
Rotorhorn,
Has a helicopter landed when it comes to a low hover? That's a really interesting one. I don't know. And if the answer's yes...what about a 10 ft hover, a 20 ft, 200 ft... What about hovering on final (if it's safe)? I suppose I could theoretically have hovered 20 ft from the south side grass, awaiting clearance to land.
Does anyone know?