The release of quarterly expenses for Government ministers - which includes credit card spending, travel and accommodation - has been delayed after a "process oversight" by the Department of Internal Affairs during collation.

The expenses, which are normally released at the same time as MPs' expenses, were due to be released today but in a statement, the department said an oversight was identified yesterday during a quality assurance, pre-publication verification process.

"A decision was made to postpone the publication so that a complete data set for the quarter is available. This will be completed with urgency, and we hope to be able to resolve this in the next two weeks," the department said.

Minister for State Services Chris Hipkins said he was frustrated at the delay in the release of the latest quarter.

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"I heard about the issue last night. It is frustrating. The process is not a new one and the Government expects better.

"I have asked for a detailed report on how the error occurred and to outline what steps will be put in place to stop this happening again," he said.

MPs' expenses for travel accommodation for the last quarter were released last Thursday, three days after National leader Simon Bridges' expenses were leaked to media early.

Parliament's Speaker Trevor Mallard today announced the appointment of former solicitor-general Michael Heron, QC to look into who might have leaked the information early.