The Prime Minister has finally brought clarity to New Zealand's post-Brexit strategy with the UK.
The 2016 Brexit vote divided New Zealand's foreign policy establishment almost as neatly as UK voters.
On one hand were those who were alarmed at the potential unravelling of an institution that has kept the peace in Europe for an unprecedented 74 years.
On the other were those who, after decades battling the European Union (EU) over its Common Agricultural Policy, celebrated Brussels' bloodied nose.
More constructively, the second lot saw the opportunity for New Zealand to be the first cab off the rank for a gold-standard free-trade agreement (FTA) with the world's fifth largest economy, with whom we enjoy close ties on everything from the Five Eyes spy network to the traditional Kiwi OE and UK gap year.
The first group scoffed at such colonial cringe, preferring to place the emphasis on the NZ-EU FTA.
The Key-English Government made no progress resolving this division or developing a strategy to gain from Brexit.
Jacinda Ardern inherited a Labour Party that had shamefully defected from the bipartisan consensus on free trade over what would become the Comprehensive and Progressive Trans-Pacific Partnership (CPTPP).
Europhiles by nature, Labour's inclination was also to lean towards the EU over the UK.
Winston Peters' NZ First also opposed the CPTPP but its relationship with Nigel Farage and his UK Independence Party made it sympathetic to a post-Brexit NZ-UK FTA.
At Peters' behest, the Coalition Agreement proposed a Closer Commonwealth Economic Relations deal which MFat has barely taken seriously.
This lack of clarity continued in government.
Ardern's big foreign policy speech in February oddly failed to mention the EU, elevating the UK to our third best friend.
Peters, while inexplicably slow to back the UK when Vladimir Putin's agents committed an act of war in Salisbury, remained a UK-phile on trade and has explicitly supported a Hard Brexit that would create the greatest urgency for the UK to negotiate new FTAs.
Meanwhile, New Zealand exporters to the UK were crying out for guidance about what rules would apply from 11pm on March 29, the moment the UK leaves the EU.
The Prime Minister cut through all this during a whistle-stop 30 hours in London on Sunday and Monday. Peters' name wasn't uttered once.
The very fact the visit even went ahead was something of a triumph.
Theresa May risked mocking in the House of Commons for giving Ardern over an hour on the very day she was required to present her Brexit Plan B.
That mocking occurred but May was able to link the Ardern meeting to the UK's interest in joining the CPTTP, the entry provisions for which were finalised by Trade Minister David Parker and his counterparts in Tokyo on Saturday.
New Zealand's pioneering role in the CPTPP, going back to the 1990s, has created a diplomatic quirk that joining the world's third largest free-trade agreement requires first writing to Wellington.
Ardern skilfully sidestepped the question of hard versus soft Brexit by publishing a column in that journal of the Tory establishment, the Daily Telegraph, headlined "Whatever Britain decides about its new place in the world, New Zealand stands with you".
While surely embarrassing to New Zealand readers, with its echo of Michael Joseph Savage's "where [Britain] goes, we go", it worked with its audience.
Ardern was of course completely in her element with the soft public-diplomacy aspects of her trip, interspersing public pitches for an FTA into interviews about pregnancy, breastfeeding and marriage proposals.
At Downing St, she and May endorsed that morning's signing of a NZ-UK Mutual Recognition Agreement ensuring all existing rules for trade between the two countries remain unchanged upon Brexit.
Most importantly, May and Ardern confirmed that a NZ-UK FTA would be one of the first three cabs off the rank, along with the US and Australia, plus the UK's interest in the CPTPP.
Privately, New Zealand trade officials indicate more progress has been made towards launching negotiations for the NZ-UK FTA than either prime minister can acknowledge publicly, given the UK is not supposed to begin such talks until it leaves the EU and New Zealand needs to remain on the right side of Brussels to complete the long-awaited NZ-EU FTA.
The Prime Minister deserves a quiet champagne on her long flight home, not least because she faces immediate decisions about what to do with her hapless Housing Minister and his KiwiBuild shambles as soon as she arrives in Wellington.
She would be well advised to demonstrate the same sense of purpose on that issue as she did on the trade issues in London.
- Matthew Hooton is managing director of PR and corporate affairs firm Exceltium.