OTTAWA – The Speaker of the Senate has shot down a Liberal bid to investigate allegations that the Prime Minister’s Office interfered in an independent audit of Mike Duffy’s expenses.

Noel Kinsella has rejected Liberal Senate leader James Cowan’s argument that the alleged interference constituted a breach of senators’ privileges.

The ruling is based on Cowan’s timing, rather than the merits of his arguments.

Kinsella says questions of privilege must be raised at the earliest opportunity but, in this case, Cowan waited two weeks to raise the matter after first learning about the alleged interference from RCMP documents filed in court on Nov. 20.

A favourable ruling from Kinsella would have sent the allegations to a Senate committee for further study.

That would have given the Liberals another chance to try to call two key witnesses alleged to have been involved in trying to tamper with the audit: Conservative Sen. Irving Gerstein and Deloitte managing partner Michael Runia.

The Conservatives have used their majority in the Senate to defeat previous Liberal efforts to have Gerstein and Runia testify.