Key details related to Peter Dutton’s decision to grant visas on public interest grounds to two au pairs in 2015 must continue to be suppressed for privacy reasons, a tribunal has ruled.

In the first case, an au pair whose visa was cancelled at Brisbane’s international airport in June 2015 was able to make a phone call and, within a couple of hours, Dutton approved a new visa using his ministerial discretion powers.

In November the same year, Dutton defied written warnings from his department that granting a visitors’ visa to a second au pair was of “high risk” because she had previously been counselled about work restrictions.

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Over the past two years, Dutton’s department has been trying to suppress key details of the cases and the reasons underpinning the decisions.

Dutton insists he does not know the two individuals involved and that they did not work for his family, but said it would have been inappropriate for them to be deported.

The minister’s office still refuses to answer specific questions about the identity of the au pairs’ employers.

AAP sought access to details surrounding the cases under freedom-of-information laws but documents supplied in 2016 were heavily blacked out because of privacy provisions.

The case went to Administrative Appeals Tribunal last month and member Chris Puplick, a former Liberal senator, on Tuesday afternoon dismissed AAP’s case.

“There is no basis for any suggestion of improper or irregular behaviour on the part of the minister of the department,” Puplick said, adding that it was mere speculation and there was no basis for the case to succeed on public interest grounds.

AAP’s lawyer Surya Palaniappan had argued the minister’s “broad and largely unfettered discretion” only served to increase the public interest in terms of finding out how it was exercised.

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Puplick acknowledged the statements to parliament regarding visas granted with ministerial discretions had become “essentially formulaic” and revealed almost nothing of the minister’s thinking in individual cases.

But he said legislation in effect imposed no greater obligation than to report the numbers.

He said releasing the full documents would be granting access to “personal information” in a way that makes the individuals “reasonably identifiable”.

“The visa grantees are most likely to have left Australia by this stage, although they are still entitled to protection of their privacy,” he said.

Puplick did not agree with AAP’s argument that the au pairs’ employers should be named on public interest grounds.

He said the information would contain highly sensitive material about the individuals and how Australian Border Force operates.

“I give no weight to the argument that there is some overriding or overwhelming public interest to be served by releasing further information,” he said. “Exactly how far this slippery concept of ‘public interest’ extends is a matter of endless and ongoing debate.”