Len Brown has given John Banks an enormous, stinging slap in the face.

And, with his overwhelming victory in the Supercity mayoral race, the south Aucklander has also given John Key's centre-right government a potential headache.

That is because yesterday's local body elections could be the biggest shift in New Zealand's political power base since the capital city was shifted to Wellington in 1865.

The man that John Key and Rodney Hide expected would take the leadership of the new Auckland Supercity - centre-right Auckland City mayor John Banks - was dealt a resounding defeat. And, most embarrassing for him, he lost by a margin of more than 60,000 to a so-called "grey man" from Manukau, a man of whom most New Zealanders had barely heard till he made the evening news slapping his own face in remorse at revelations of his personal spending on the council credit card.

It was an election campaign that was also marred by allegations of electoral fraud: a Labour candidate from south Auckland, Daljit Singh, is now facing charges.

Brown's wife was diagnosed with cancer during the campaign, while Banks' son was revealed to have encouraged another teenage boy to drink so much alcohol that he lapsed into a coma and died. But all of that is history now: On November 1, Len Brown will become the first mayor of Australasia's biggest civic authority, with a population of 1.4 million.

That means that he wields a power weighty enough to provide a partial counterbalance to that held by the Prime Minister in Wellington.

At 4.30pm yesterday, John Key was forced into the embarrassing position of addressing media about the election results, without having spoken to the mayor elect.

The prime minister had left a message on Brown's cellphone voicemail at 2pm and Brown had not yet got round to returning his call.

Nonetheless, Key gave the new mayor due credit: "He's set out a vision for Auckland and we look forward to working with him on that vision and building what we believe is the potential for a world-class city," the Prime Minister said. "He has the overwhelming support of the people...and I'm confident he can do a good job. It's a big task in front of him."

And after Brown's credit card embarrassment, that word - "credit" - could be the theme of his next three years.

If Brown is to deliver on promises such as a rapid transit system through the city, rail out to the airport and free entry to council swimming pools, he will have to put much of it on tick.

In addition, the council hasn't been told what the bill will be for a leaky homes solution nor for the merger of the eight councils - Rodney, North Shore, Waitakere, Auckland, Manukau, Papakura and Franklin with the Auckland Regional Council.

And, with no review of rating due till 2012, it is likely that the new Supercity will have to run up more public debt to pay for its new infrastructure.