Prime Minister Stephen Harper has filed a $2.5-million libel suit against the Liberals over statements published on the party's website alleging the Tories offered a bribe to the late Independent MP Chuck Cadman.

Harper announced during Thursday's question period in the House of Commons that his representatives had filed a statement of claim on his behalf in court, in what he said was an action "any Canadian would do when he has been unfairly treated."

A copy of the statement of claim obtained by CBC News lists the Liberal Party of Canada, the Federal Liberal Agency of Canada, as well as Jane Doe and John Doe — the as-yet unidentified authors of content published on the Liberals' website.

"For the past couple of weeks, both inside and outside of Parliament, the Liberal party and its agents have been making allegations against me that are of a criminal nature, that are absolutely false and that are despicable," Harper said.

"I have every right, as does my family, to defend our reputation, and Mr. Speaker, the Liberal party will come to regret engaging in this illegal and untruthful behaviour."

But Liberal Leader Stéphane Dion said his party would not apologize and continued to press Harper in the House about what, exactly, the Conservative party offered Cadman in spring 2005 to vote against the then Liberal government of Paul Martin.

"Will he admit the only thing transparent about his government is that Canadians can see right through it?" Dion asked.

Harper not taking responsibility: Liberal leader

Dion again accused Harper of dodging responsibility over what he said on the matter in a recorded conversation with a journalist shortly after Cadman's death in 2005.

Harper responded by saying only an "incomplete and edited version" of the conversation was released.

In the tape, Harper is heard being asked by Vancouver journalist Tom Zytaruk about an offer of a million-dollar insurance policy.

"I don't know the details. I know that there were discussions," Harper replies on the tape.

Liberal Deputy Leader Michael Ignatieff said the prime minister "won't be able to evade Canadians the way he's evaded this House.

"He won't be able to threaten them with lawsuits," Ignatieff said.

The Conservatives maintain that two representatives from their party met with Cadman ahead of the vote, but he said they only offered him the party's nomination to run for re-election in his Surrey, B.C., riding, and funds for the campaign.

Cadman, who died two months after the meeting with Tory officials, is at the centre of allegations the Conservatives tried to bribe him to secure his co-operation on a crucial budget vote that threatened to topple the Liberal minority government in May 2005.

In Zytaruk's soon-to-be-published book, Like a Rock: The Chuck Cadman Story, his wife, Dona Cadman, alleges the Conservatives offered her husband a million-dollar insurance policy if he voted to bring down the Liberal government.

Two Cadman children have also said their father told them of the offer.

On the crucial day, the Independent MP sided with the Liberals, allowing them to survive the narrow confidence vote. If the Liberals had lost the vote, the government would have fallen and an election would have been called.