Writing in The Guardian, Hager, who had previously published a book called ‘Dirty Politics,’ which exposed the extent of the National Party’s links with a conservative blogger, said: ‘New Zealand’s National party resoundingly won a third term in government on Saturday, despite revelations in my recent book about a dirty tricks campaign run from the prime minister’s office.

‘But as the voting results showed, it’s arguable that the dirty tricks had already worked, smearing and destabilising political opponents and paving the way to victory.

‘Key’s political opponents have been painted as dodgy, untrustworthy or incompetent. It was no surprise at all that he has stayed high in the polls and won the election.’

The whole election campaign was dogged by allegations of dishonest behaviour, smearing and of mass surveillance, which forced one senior minister to resign.

Key denied any wrongdoing and campaigned on the government’s strong economic record.

The National party won with 48.1% of the vote, giving it 62 of 121 parliamentary seats and improving its performance on the previous vote in 2011.

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