Blogger Cameron Slater, lobbyist Carrick Graham and former MP Katherine Rich have failed in their bid to have hacked emails excluded from a defamation case.

The High Court has also ruled that Slater and Graham will have to take the stand to be "orally examined" pre-trial, as their written answers so far have been "inconsistent".

And all three defendants have been ordered to provide more paperwork to the plaintiffs - a trio of health experts - particularly around what payment agreements were made between them.

The case - in which health academics Douglas Sellman, Boyd Swinburn and Shane Bradbrook have sued for defamation - arises from a series of blog posts between 2009 and last year, and was prompted by revelations in the 2014 book Dirty Politics.

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Slater, who writes the WhaleOil blog, is accused of being paid to write the posts by ex-National MP Rich through her employer the Food and Grocery Council (NZFGC).

They accuse Graham, son of the former National cabinet minister Sir Douglas Graham, of being the middle man.

Previously, the defendants tried to get the case struck out, but the court declined.

A jury trial should go ahead next year; High Court Judge Matthew Palmer issued a second judgement on preliminary matters before trial today.

In it, the judge declined Slater's application to exclude hacked documents obtained by the plaintiffs from Nicky Hager - the author of Dirty Politics - at this stage.

He also said the defendants had not complied with discover. While Slater disclosed 32 documents, other than blog posts, including 27 individual emails to or from Rich - there was no evidence of payments received and only one document containing data from the Whale Oil website.

Graham disclosed 172 documents including four emails from Slater and 114 emails to or from Rich or NZFGC. None of the discovered emails to or from Rich pre-dated the publication of Dirty Politics, the judge said.

Rich and NZFGC disclosed around 1200 documents, including 24 items of correspondence with Graham. No correspondence with Slater was included.

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The judge said there were grounds for believing Slater and Graham had not provided some documents, and requested they be provided.

Some documents about payments were included, revealing the fact Graham's company received $365,814 from NZFGC over about five years.

But he wanted a more precise account of the terms and scope of services between Rich and/or the NZFGC and Slater or Graham including any associated documents.

He said the hacked emails would not be struck out because he was not persuaded they were not genuine.

After examining Graham and Slater's answers to interrogatories, the judge said he was concerned their statements that WhaleOil did not publish blogposts for reward were "not consistent" with the plaintiff's evidence.

"They are inconsistent with reasonable inferences from the emails obtained by the plaintiffs," the judgment said.

"I am also concerned a number of other aspects of the interrogatories may not have been properly responded to, regarding: who was the author of the blog posts; the involvement of each of the defendants in their preparation; downloading of blog posts; authorship of the comments; and payments received. I consider Mr Slater and Mr Graham have made insufficient answer to the interrogatories. "

He said the pair would be required to take the stand for up to an hour during pre-trial.