When Jacinda Ardern became the leader of a ravaged and desperate New Zealand Labour party seven weeks ago, she promised to run a “relentlessly positive” campaign. The party, which had fallen as low as 23 per cent in the polls, was staring white-eyed at another electoral thrashing. Her first job was life support.

But Ardern achieved the apparently impossible: Labour overtook the governing National party in the polls, turning a 20-point deficit into a four-point lead. Her party’s policy was essentially unchanged, but the new leader suddenly had the ear of the country. Measured against the stern competence of the prime minister, Bill English, Ardern’s approach was a breath of fresh air. The media hailed Jacindamania, Jacinda-anything: an all-purpose suffix for any superlative.

National, chasing a fourth term — a feat only achieved once before in New Zealand— struggled to find a way to counter a new, optimistic opponent. In her only significant mistake of the campaign, Ardern provided it for them.

Her only substantial change in policy was to leave open the possibility of changes to the tax system, whereas her predecessor, Andrew Little, had pledged that any recommendations from a working group would not be introduced in a first term. Almost immediately Labour’s “Let’s do this” slogan was pilloried by National in “Let’s tax this” attack ads. A campaign that had been focused on issues such as the housing crisis, child poverty and health, instead became focused on the economy. Ultimately, Ardern reversed her “captain’s call” and kicked the can of tax changes back into the long grass.

“Jacindamania”, of course, owes something to the British Labour experience under Jeremy Corbyn. And English’s conservative campaign sounded a lot like that of Theresa May, too. In his speech late on Saturday night, after the vote count gave National a lead of more than 10 percentage points over Labour, English was reading directly from the May script: “We have the responsibility to deliver strong and stable government.”

Under New Zealand’s proportional representation system, however, National is not guaranteed to lead the next government. Labour will edge closer once special votes are counted. But English, who succeeded John Key as prime minister late last year, has overcome the demons of his last shot at leadership, which ended in a humiliating defeat in 2002, and is easily the best placed to form a coalition government. The balance of power will be held by Winston Peters, the leader of the New Zealand First party. One senior National MP who remembers Peters’ previous role in a National-led government in the 1990s, recently told the Guardian that working with him was like “being stuck in a cage with a possum”.

The charismatic and irascible figure , recently witnessed proselytising to a rally of farmers beneath a giant fibreglass cow in Ardern’s home town of Morrinsville, has indicated he will talk first with the largest party. A National-NZ First arrangement is the most likely outcome by some stretch.

Speaking to the party faithful in Auckland on Saturday night, Ardern left open the possibility of a change of government, saying: “I simply cannot predict at this point what decisions other leader will make.” But a Labour-led government, incorporating both NZ First and the Greens, remains a long shot. As well as fibreglass cows, the campaign had its share of bullshit. National’s attack on Labour was effective, but heavy on post-truth politics. The media were summoned to witness an “$11.7billion hole” in Labour’s fiscal projections, only to find there was no such thing; not so much as a single independent economist to back up the claim. A similar line was run on income tax. Labour would increase it, ran the National attack ads, though in truth Labour’s plan was to simply not put National’s pledged tax cut into effect.

English — in contrast to his joke-cracking predecessor — built a reputation as a laconic and serious-minded finance minister under Key, even earning the sobriquet “Honest Bill”. He has picked himself up after the humiliation of 15 years ago, and will very likely run the next government, unscarred by his embrace of bullshit.

For her part, Ardern pledged on Saturday evening: “I can assure you we will remain relentlessly positive.”

— Guardian News & Media Ltd

Toby Manhire is a former editor of the Guardian comment pages.