On 29 June 2023, the Immigration Rules were updated and it is now confirmed that citizens of New Zealand who hold a Youth Mobility Scheme (YMS) visa can extend their visa for one year by submitting an online form.
They will need to pay £259 for the application fee and £470 for Immigration Health Surcharge.
They can extend their visa only once and the new leave will be valid from the day after the original visa ends.
The processing time of the application would be 8 weeks and you may be able to use the priority service.