If you look on the universtiy web sites, each have a section of internation student entry criteria. this of course includes UK 'A' levesl which are different to Cambridge 'A' levels here.
With regards to course fees and loans, the rules have just changed here to make the crietria for being treated as a national student tougher. I think it's now you have to be a resident for a full two years to be treated as a Kiwi student.
At the moment student loans are zero interst and can be repaid over a far longer period than the UK.
Finally although NZ uni's don't rank in genral as highly as the 'better' UK unis they are very much not a second class choice. They have excellent business and accademic reputations worldwide, indeed some people like their more tradtional approach to courses and content (me inlcuded)