They were trying to locate a woman who had appeared in a video they were investigating.
That woman had a New Zealand accent and distinctive tattoos.
The video, filmed in about 2017, showed a boy aged between 6 and 9 months being sexually abused.
Police here were told that identifying the woman who appeared was "pivotal to identifying the young boy" who would now be about 4.
The UK investigation is ongoing.
The Herald learned about the hunt for the woman last week.
Police said they were "close" to identifying and locating the woman and asked for a delay in publication so as not to tip her off.
She was arrested days later.
The investigation here was undertaken by the Online Child Exploitation Across New Zealand (OCEANZ) team - a specialist team working to protect children from online child abuse.
Police confirmed the woman was arrested following the execution of a search warrant which was initiated from information provided by "international partners".
As the matter was before the courts the could not comment further.
The Herald reported last week - following the guilty pleas of two Waiuku men on charges of child exploitation material - that there has been a massive increase in demand for child pornography which has increased by at least 1500 per cent since 2007.
In New Zealand, over a million clicks on illegal child sex abuse websites were identified by the Department of Internal Affairs through a two-year trial period ending in 2009.
"There is an increasing trend towards younger victims and greater brutality. "An estimated 20 per cent of all pornography traded over the internet is child exploitation material and since 1997 the number of child exploitation images on the internet has increased by 1500 per cent," police told the court in the case of the Waiuku pair.
"The figures are concerning - but are a correct reality of the offending across New Zealand.
"The internet is a worldwide, easy access source of information and a major gateway for offenders to access child exploitation material for sexual gratification."
HOW TO REPORT ONLINE CHILD ABUSE
New Zealand Police have a specialist team working to protect children from online child abuse — the Online Child Exploitation Across New Zealand (OCEANZ) team.
OCEANZ liaises directly with anyone who reports online child abuse.
And they will provide advice on what you need to do and how police will investigate your complaint.
If you know of anyone with child exploitation material or you have concerns about online child abuse - you should make an online report directly to OCEANZ.
