Claims of dirty dealings within New Zealand’s National Party are shaking the reputation of once squeaky-clean Prime Minister John Key.

Investigative journalist Nicky Hager’s latest book, Dirty Politics, details the way government figures have directed public attacks against their political opponents since 2005, as well as the government’s close relationship with right-wing blogger Cameron Slater.

The book is based on thousands of emails hacked from Slater’s computer, and is not the first time Hager has targeted the National Party’s media strategy with a pre-election expose: this one was launched five-and-a-half weeks out from the September 20 parliamentary election and has forced “Teflon John” Key off message.

Key is struggling to distance himself from the mounting scandals, with the two main debates involving Justice Minister Judith Collins and revelations of irregularities around Slater’s Official Information Act (OIA) requests.

Collins has already admitted to allegations in Dirty Politics that in 2009 she gave Slater the name and contact details of Internal Affairs official Simon Pleasants. She suspected the bureaucrat — wrongly — of leaking information to journalists, and he ended up receiving death threats after his name was published on the Whaleoil blog alongside the allegations.

Collins is already on thin ice after a series of political blunders this year, including secretly visiting the Shanghai offices of dairy company Oravida, of which her husband is a director, and admitting she knew 700 burglaries in south Auckland had been downgraded so they wouldn’t appear in crime statistics.

The other scandal Key is trying to hose down is claims the prime minister’s office and Collins helped Slater with OIA requests. Hager claims that in 2011 Key’s staffer Jason Ede advised Slater to request documents from New Zealand’s spy agency, the Security Intelligence Service (SIS). These documents proved the then-Labour leader Phil Goff had indeed been briefed — despite his denials — about suspected Israeli spies caught in the Christchurch earthquake, and Slater used that information to embarrass the politician.

Although Slater’s request was approved, the same application by Wellington’s Dominion Post was refused. The spy watchdog is now investigating why the blogger was favoured over the media outlet.

Key, head of the SIS, denies he knew of Slater’s request.

This was called into question last week when radio station Newstalk ZB released a letter dated November 9, 2011, from former SIS director Warren Tucker saying: “I notified the Prime Minister (in accordance with my usual practice to keep the Minister informed on a “no surprises basis) [sic] that I was going to release redacted documents in response to the request from Mr Slater.”

Documents released over the weekend by the New Zealand Herald also suggest Collins may have expedited two OIA requests from Slater, with one request being met in five hours and the other in 37 minutes.

Disclosures in Dirty Politics are being backed up by the release of the leaked emails via the Twitter account @whaledump. Hager welcomed the release and said the leaker was acting after he requested some of the original emails to publicly support the book’s claims.

The last time Hager landed the National Party in hot water before an election was in 2006. A week before the vote he released his book The Hollow Men, which, also via leaked emails, detailed the backroom dealings of the National Party with big business and the religious sect the Exclusive Brethren, in order to swing public opinion away from Helen Clark’s administration.

In 2002, Hager cornered the Labour government over the accidental release of genetically modified seeds into the country.

The accusations in Dirty Politics are serious, but so far the response from Key has been to label them a smear campaign and part of a “left-wing conspiracy”.

And yet in spite of the bomb Hager has set off under National, the party is still polling at 50.6%. Its nearest rival, Labour, is trailing with 26.4%.