Two Opposition parties are calling for an investigation into Prime Minister Paul Martin's role in the secret talks between senior Liberals and Tory MP Gurmant Grewal.

Bloc Quebecois Leader Gilles Duceppe said he has asked the RCMP to find out when Martin authorized his chief of staff Tim Murphy to talk to Grewal.

Duceppe says because it is a criminal offence for an MP to sell his vote, it is necessary to find out whether Martin authorized Murphy to continue negotiations after he found out Grewal was willing to cross the floor in return for a plum post.

Meanwhile, NDP Leader Jack Layton has also asked Parliament's ethics commissioner, Bernard Shapiro, to investigate the prime minister's role in the matter.

Layton said he requested the probe after Bernard Shapriro concluded that Murphy is out of his jurisdiction as he does not hold public office.

Meanwhile, Grewal's wife Nina, also a Conservative MP, broke two weeks of silence to say she had nothing to do with the secret talks.

Grewal tells the Toronto Star that she was not approached by the Liberal Party ahead of the May 19 budget vote, nor did she take part in any negotiations with the Grits.

Grewal's husband has been dogged by controversy since he revealed secretly taped conversations with Health Minister Ujjal Dosanjh and Murphy.The Liberals say the tapes were altered and conversations omitted from the transcripts.

Grewal is also alleged to have broken airport security rules when he asked strangers to transport new tapes of the full conversations on a flight to Ottawa.

Air Canada is investigating the incident and Grewal is currently on stress leave.

On the tapes, Gurmant is heard talking about a Senate appointment for his wife. He claims to have consulted her about switching parties, but adds "we are not decided, we have not made up our minds yet.''

Despite her husband's withdrawal from the political scene, Nina Grewal says her husband is feeling fine.

"He's in high spirits,'' she tells the paper. "We're both still fighting for the right cause.''

Meanwhile, a new poll finds that the Conservatives' decision to release the secretly taped conversations to embarrass the Liberals fell flat.

A poll by Decima Research found that respondents were slightly more inclined to believe the Liberal explanation -- that Grewal approached them and asked for an appointment -- than the version offered by Grewal: that the Liberals came to him.

The poll of 1,000 respondents conducted from June 2 to June 5 found that 25 per cent of respondents sided with the Liberals, compared to 23 per cent who said they believed Grewal.

In B.C., where Grewal and his wife have their ridings, 33 per cent believed the Liberals and just 21 per cent believed Grewal.

Conservative leader Stephen Harper continued to insist Wednesday that it's the Liberals who are fabricating the truth.

"Everything on those tapes and I've seen Mr. Grewal do since is consistent with his story," Harper told parliamentary reporters.

"On the other hand, as I point out, everything the Liberals have done since has been a series of evasions, fabrications, changing of stories and outright lying."

With files from The Canadian Press