National has written to the State Services Commissioner asking for the investigation into Treasury's website security to be widened to include "serious questions" about both the department's and the Finance Minister's behaviour.

The party's deputy leader, Paula Bennett, said there are still many unanswered questions that need to be addressed.

Last week, after National released Budget information ahead of its scheduled release, the Treasury said it had been "hacked".

Finance Minister Grant Robertson called on National to stop releasing information "given that the Treasury said they have sufficient evidence that indicates the material is a result of a systematic hack and is now subject to a Police investigation".

But, as it turned out, Treasury was not hacked and National obtained the information through a simple search of the department's website.

Robertson said he was "disappointed" that the information could be accessed in this way.

National leader Simon Bridges said Robertson's statement had clearly implied National had hacked Treasury, or had received hacked information.

In a letter, dated May 31, Bennett said the saga raised "serious questions" about the politicisation of the public services – implying that the Government used Treasury to smear the National Party.

Robertson has rejected this accusation.

A spokesman for the State Services Commission (SSC) confirmed on Friday that an inquiry would look into Treasury and issues around its website security.

SSC boss Peter Hughes is considering the allegations made by Bridges around whether Makhlouf smeared National, or misled the Minister of Finance.

At this stage, however, the SSC spokesman said that was not part of the official inquiry.

But Bennett said that needed to be part of the official investigation.

She wants Robertson's role in the saga to be looked into, as well as a complete review of all communications between the Finance Minister's office and the Prime Minister's office under the "no surprises" approach.

What information Treasury and the Finance Minister had at their disposal before they issued those statements also needs to be investigated, Bennett said.

"The actions of the Secretary to the Treasury and the Minister of Finance in misleading the public in this way have had a detrimental effect in maintaining public confidence in a neutral public service that works without political influences," Bennett said in the letter.

"Without a full investigation that covers the issues I raised, it risks derailing the years of progress New Zealand has made as a world-leader in Open and Transparency."

The SSC and Robertson have been approached for comment.