Before 2019 British passport holders or British citizens could travel to New Zealand for a period of 6 months without requiring any Visa.
Since 2019 New Zealand eTA (NZeTA) has been introduced which requires British Natinoals to apply for a New Zealand eTA (NZeTA) to enter the country. There are numerous benefits to New Zealand including collection of International Visitor Levy fee to support the burden on natural visitor sites and upkeep. Also, British nationals will avoid the risk of being turned back at the airport or seaport because of any past offence or criminal history.
New Zealand eTA (NZeTA) application process will check the issues upfront and will either reject the applicant or confirm. It is an online process and the applicant will receive the response via email. That being said, there is a cost to be incurred by the UK passport holder or any national for applying for a New Zealand eTA (NZeTA). All nationals can visit New Zealand for a period of 3 months at a stretch on New Zealand eTA (NZeTA) but British citizens have the privilege to enter New Zealand for a period of up to 6 months on a single trip on a New Zealand eTA (NZeTA).