UK Ancestry: One more question.

[Sumac]

Hi,

I have a 5 year Ancestry visa which expires in Sept 2019. I spent just over a year living and working in the UK before returning home to New Zealand for family reasons, and it is now my intention to return in March next year to see out the remaining 18 months (and then likely apply for a new visa). An answer to an earlier question to this forum suggested that returning after a 2 year absence would be fine and the visa wouldn't have "timed out" in my absence. However, by the time I return I will have a new passport (NZ passports were only valid for 5 years when I first applied for the Ancestry visa). Will arriving in the UK with my still-current visa inside an expired passport cause me any problems when I reach the border? It seems like a minor thing to worry about, but I'd hate to get turned around at LHR just because I needed to fill in some forms or tick some boxes here in NZ before departing.

Any advice gratefully received, thanks.