In your application form you will be asked to declare any criminal convictions or pending charges. The Criminal Records (Clean Slate) Act 2004 means those who have had no convictions within the last seven years, and who meet other criteria in the Act, don’t have to disclose any convictions.
However, in the case of applying for front line roles (working with offenders) Clean Slate DOES NOT apply and you are required to disclose ALL criminal convictions you have had regardless of when those convictions occurred. You can find out more about criminal records and the Criminal Records (Clean Slate) Act 2004 on the Ministry of Justice website.