OK here we go - I flew in NZ for 2 years.
I went there with a UK JAR PPL - I was required to do 1 hour of low flying, 5 hours of instrument flying, 1 hour of mountain flying, 5 hours of additional 'handling' for the NZ PPL.
Back in the UK you will find that the NZ PPL requires you to complete a skills test and whatever other 'familiarisation traing' (nav etc) the FTO requires but overall you'll not be required to do much more to convert.
Hope this helps
Arc