The government is refusing to release documents relating to its trouble-plagued $200m regional grants program, claiming release would not inform debate on a “matter of public importance”.

Refusing a freedom of information request for written briefings that informed the government’s allocation of grants in the lead-up to the May election, the department claimed a range of exemptions, despite agreeing that disclosure would allow “some oversight of public expenditure”.

The government has come under fire for its management of the regional jobs and investment packages (RJIP) program, after the auditor general tabled a scathing report on Melbourne Cup day that found ministers had knocked back almost 30% of recommended projects and supported 17% of those not recommended.

The refusal to release documents, in response to a freedom of information request from Guardian Australia, states that advice was also sought from the Department of Prime Minister and Cabinet about the release, with Scott Morrison’s department advising that the documents would reveal cabinet decisions.

The department said the documents contained “opinion and advice” prepared for the minister as well as assessment and scoring methodology associated with the RJIP funding package.

“This information is considered to be deliberative in nature. If this information were released it could reasonably be expected to provide insight into the deliberations of the department.

“In particular, the briefs contain details on the methodology used by the the department regarding how it assesses, scores and ranks applications under the RJIP package.

“I am of the view that this information should not be released as it would provide insight into how this package, as well as potential future funding programmes, are assessed within the department.”

One of the criticisms of the government’s management of the program is that the ministerial panel ignored the department’s ranking of projects when it awarded the funds.

In one instance the top eight projects recommended for funding in the Wide Bay-Burnett region, based on the department’s merit-based scoring system, were knocked back for funding, while two known political donors to the Liberal National party with a lower score were successful.

The authorised freedom of information officer who made the decision to reject the FOI request was Donna Wieland, the department’s general manager of regional programs, who also provided advice to the infrastructure minister, Michael McCormack, about how to avoid providing documents in response to a Senate order.

The refusal also claimed that the privacy and business affairs of applicants were also grounds for refusing release of the documents.

“I consider that releasing information relating to RJIP applicants could reasonably be expected to result in applicants being hesitant to provide information to the department in future, if these documents were to be disclosed routinely through the FOI process,” the rejection letter says.

Guardian Australia has reported on a range of projects that have raised questions about the rigour of the RJIP application process, including a project on the New South Wales south coast that attempted to raise money for an aquaculture farm through a fish-based cryptocurrency.

A camper trailer company in the same region won a grant while it was possibly trading insolvent, while in Queensland a company that received a grant for a ferry project is losing money and the project is unlikely to happen for two more years.

In another case a former Nationals candidate secured a $300,000 grant under the scheme.

Labor’s shadow regional development minister, Catherine King, criticised the failure to release the documents as an example of the deputy prime minister, Michael McCormack, “treating the people of Australia with absolute contempt”.

“Again the government is hiding critical documents from the Australian public which relate to the expenditure $220 million of taxpayer funds,” she said.

“FOI rules are in place to allow for proper scrutiny of government decisions, but here we see the government using them to hide information from the Australian community.”

The government is bracing for another auditor general report into the Community Sport Infrastructure grants program, which saw applications recommended by Sport Australia rejected by the Nationals deputy leader, Bridget McKenzie, when she was sports minister.