No JAR schools in NZ.
You'll have to do all the JAR ATPLs, JAR CPL flight test and IR flight test. There's a compulsory 15 hours of dual before you can sit the JAR IR, and while there's no compulsory dual for the CPL it does have to be done in a "complex type" ie something that's retractable with a CSU, and you're unlikely to have one of those on your licence if you've just got a fresh kiwi CPL.
Total cost of conversion will be at least 5,000 pounds and potentially a lot more, the first time pass rate on the JAR IR flight test is only about 35 or 40%, it is the hardest flight test on earth in my opinion. Oh yeah and the ATPL theory exams are complete bastards as well
Better to just stay down under in the short / medium term in my opinion ... there's sweet FA in the way of jobs in the UK at the moment, and well founded rumour says that Air NZ are about to do some large scale hiring for the first time in decades - could really clean out the regionals down here and open up some jobs for low timers, if it's true.