Yeah Tauranga is a bit of a hike from Taupo, but I appreciate the offer all the same.
I got under it today and did as suggested above, I was by myself so it was a bit hard to move the wheel and try and see what was moving around at the same time, but what I could see when I turned the wheel, simulating turning a corner, was that the end of the connecting rod where the tie rod and the idler arm connect, would move up and down vertically instead of what I'd imagine should be on a horizontal plane. When I followed it back to the steering arm it looked as if the connecting rod moved up vertical enough it would drag the bottom of the steering knuckle over on full lock which would cause the disc to hit the control arm.
From what I could see it's the bottom ball joint that would be causing all of this to happen (just as everyone has suggested) as it's allowing the bottom of the steering knuckle to move over too much. The steering lock tabs are still there so it's not them.
I hope my explanation makes sense, it was a bit hard to try and get it all down in to words.
Anyway, I might have it all wrong, but I'm going to replace the bottom ball joints and see what happens from there. I'll keep everybody posted.