A Conservative senator is miffed that she's being asked to justify claiming a meal expense while travelling when she could have eaten a free airline breakfast of "cold Camembert with broken crackers."

Nancy Ruth says that's the level of detail she's been subjected to by Auditor-General Michael Ferguson, who is conducting a comprehensive audit of senators' expenses.

Ferguson was invited by the Senate last year to conduct the audit following embarrassing revelations about allegedly improper expense claims by Conservative senators Mike Duffy, Patrick Brazeau and Pamela Wallin and Liberal senator Mac Harb, who has since resigned.

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Duffy, Brazeau and Harb have all been charged with fraud and breach of trust; the RCMP investigation into Wallin's expense claims is continuing.

Ferguson is expected to release the results of the audit in June.

Some senators have been grumbling privately for months about the intrusiveness of the audit and expressing fears that Ferguson doesn't understand the nature of the work they do.