OTTAWA - A New Democrat MP has asked Canada's elections watchdog to expand its probe into alleged Conservative campaign spending fraud to look into transactions used to pay for public opinion polling during the last election.

Winnipeg MP Pat Martin said Monday that the strategy to have 51 candidates pay for polling - only to be reimbursed later for those expenses by the central Tory party - appears similar to the so-called in-and-out scheme the Conservatives used to funnel advertising expenses through local ridings.

"Laundering federal campaign spending through individual campaigns in order to exceed the party's spending limits is cheating, plain and simple, and there should be severe consequences for any political party found guilty of such a fraudulent practice," Martin says in a letter to chief electoral officer Marc Mayrand.

"It compounds the offence if the local candidates then claim the rebate on these false expenses."

Elections Canada is already investigating the advertising expenses claimed by 67 Tory candidates in the last election. In an affidavit in support of an RCMP raid on Tory headquarters last month, the independent agency alleges that the scheme allowed the national party to exceed its spending limit by $1.3 million and allowed candidates to claim rebates on expenses they didn't actually incur.

The Tories insist the transactions were entirely legal and that other party's commonly do the same.

"Under Elections Canada's rules, local campaigns can purchase services from the national parties," said Conservative MP Pierre Poilievre.

In this case, candidates purchased voter identification services from the national campaign. These candidates reported all of this to Elections Canada in 2004 and 2006. Elections Canada approved these as legitimate expenses."

Martin acknowledged that other parties sometimes pay for polling done in ridings. But he said there are several things that make him suspicious of the way the Tories did it.

For one, the amount of money candidates claimed for polling expenses - as much as $20,000 - seems too high for a poll conducted in one riding. Martin said he consulted a polling firm and was told that a 20-question survey of 400 people in one riding would cost about $4,000.

"I think they're misrepresenting the value of the polling," Martin said in an interview.

Moreover, Martin questioned why many of the transactions occurred months after the Jan. 23, 2006, election.

For instance, Finance Minister Jim Flaherty's financial return shows that Flaherty's campaign paid the party $15,000 on April 1, 2006 for polling. On May 25, the party transferred $15,000 to Flaherty.

Flaherty's return has been reviewed and approved by Elections Canada.

Still, Martin said it appears to him that the Tories realized after the campaign that they'd exceeded their national spending limit and looked for ways to offload some of their polling expenses on individual candidates.

NDP Leader Jack Layton raised the issue in the Commons but did not get a direct reply.

Prime Minister Stephen Harper gave the stock answer his government has given repeatedly to questions about the advertising in-and-out scheme, contending that all other parties have made similar transfers back and forth between headquarters and local riding campaigns. He pointed out that Robin Sears, a former federal secretary of the NDP, has said there's nothing unique in what the Tories did.

Layton countered later that it's only the Tories who've been raided and whose spending practices are under investigation.

Outside the Commons, Liberal Leader Stephane Dion and Bloc Quebecois Leader Gilles Duceppe joined the NDP in expressing concern about the Tories' polling expenses.