OTTAWA - Prime Minister Stephen Harper is invoking parliamentary privilege to indefinitely delay giving a deposition in a defamation suit launched by a longtime Conservative party member.

Alan Riddell is suing Harper for allegedly libelling him in the media during the last federal election. Harper's Ottawa-based lawyer, Rick Deardon, said Tuesday the prime minister is invoking parliamentary privilege to delay a pre-trial examination scheduled for no later than August. The development means Harper might never have to give a deposition.

Other Canadian courts have ruled that parliamentarians are not compelled to appear at legal proceedings while the Commons is in session, as per parliamentary convention.

Making matters even more tricky is that those same Commons customs stipulate that the privilege extends to 40 days after the end of one session, and to 40 days before the beginning of the next, narrowing the time window when an MP might be compelled to testify.

Sessions end when elections are called or when the government clears the legislative decks and prorogues parliament.

Whether parliamentary privilege will protect Harper from appearing at the actual defamation trial scheduled for next February will be hashed out in court.

Invoking parliamentary privilege is nothing new. Prime Minister Jean Chretien used it to avoid testifying at the trial of a man who threw a pie in his face, as well as at the Samson Cree's trial against the federal government. He eventually appeared in that case after he left politics.

Former Industry Minister John Manley also used it to avoid the courthouse in a suit brought by a technology firm.

"It is well-known that Mr Riddell has launched several lawsuits against the Conservative party and party officials, including Mr Harper," said Harper spokesman Ryan Sparrow. "The party and its officials are defending themselves against these lawsuits. The rules of privilege are well-known and are available to all members."

The Riddell deal

The defamation case is just part of a many-headed legal beast all connected to a deal the party struck with Riddell in November 2005.

Riddell had intended on running in the riding of Ottawa South, but was asked by Conservative party brass to step aside in favour a higher profile candidate. Riddell agreed, as long as the party paid for his expenses. The party ultimately refused to pay after Riddell spoke about the deal publicly - something they said breached an unwritten understanding of confidentiality. Liberal David McGuinty won the riding easily.

An Ontario Superior Court judge has since upheld Riddell's view of the agreement and told the party to pay his expenses and enter arbitration to discuss payment of his legal fees.

But Harper was quoted in the media during the last election saying that there was no deal with Riddell - spurring the defamation suit.

Riddell is also suing party president Don Plett for also allegedly libelling him to reporters.

Riddell said Tuesday he's approached the party at least 10 times to urge them to settle their difference quietly and inexpensively out of court, to no avail. The parties are still discussing a potential settlement.

"I find these proceedings very embarrassing. I'm someone who worked for 25 years for the Conservative party...and I'm very disappointed by the way that things have proceeded," Riddell said outside the Ottawa courthouse. "I think that this was unnecessary that it got to this point."

The Conservative party is currently appealing the Superior Court ruling that found the agreement to pay Riddell binding.

All this comes against the backdrop of another trial involving Riddell, one specifically studying whether or not he breached a confidentiality agreement in the deal with the Conservative party. In this case, Riddell is the defendant.

The party successfully convinced a judge Tuesday to delay the trial until a new date can be agreed upon.

Riddell's lawyer Tom Conway said the party has "painted itself into a corner" by maintaining that such an agreement involving electoral candidates should be secret.

"It's afraid its witnesses will appear like cigar-smoking backroom boys," Conway told the court. "That is a political problem for them but it's not a legal problem."