Former NDP leader Ed Broadbent says he's concerned about the direction Thomas Mulcair would take the NDP if he wins the leadership and he questions his commitment to social democratic values.

Broadbent didn't hold back on his assessment of Mulcair, who is considered a front-runner in the leadership race, during an interview with Rosemary Barton on Power & Politics on Thursday.

He said the candidate he is backing, Brian Topp, is clear when he talks about keeping the NDP firmly rooted in its social democratic roots and his tax policy is an example of that commitment.

Equality is a core value for the NDP and when social democrats see problems, they react with policies, he said.

Asked whether Mulcair understands what a social democratic party is all about, Broadbent said, "I don't know, that's what I don't know."

He said there is a perception that Mulcair wants to move the NDP toward the centre, a direction Broadbent said would be wrong and counterproductive. The NDP will win government by drawing more people away from the centre, he said.

Broadbent said a Mulcair victory won't necessarily mean New Democrats are rejecting Topp's vision in favour of Mulcair's.

"I'm not sure of that because many are not sure what Tom would really like to do," he said. They see a successful and forceful MP, he said, but, "They don't know where he would stand on the inequality issue."

Party modernized under Layton

"They may have some hunches one way or another, but it has to be spelled out. They don't know where he is in terms of building a team and holding a team together in a coherent fashion, which is a big challenge for leadership especially when you're in opposition," he said.

Broadbent said his biggest problem with Mulcair is his suggestion that the party hasn't been moving in the right direction and hasn't been modernizing properly for some time.

But it was former leader Jack Layton who came up with the strategy to target Quebec, where Mulcair won a byelection in 2007 to become the province's only NDP MP at the time, and transformed how the party grew its membership and raised money, Broadbent said.

"There was a presumption that the party wasn't modernized before Tom started talking about it. It was modernizing, that's why we had the sweep in Quebec under Jack's leadership," he said.

Mulcair talks about modernizing the NDP but hasn't been specific about what he wants to do, according to Broadbent.

The ongoing leadership race was prompted by Layton's death in August. Mulcair and Topp are battling it out for the job with Nathan Cullen, Niki Ashton, Paul Dewar, Martin Singh and Peggy Nash.

Topp is known for his backroom work with the NDP. He was Layton's campaign director in 2006 and 2008 and was also involved in the 2011 election.

Broadbent said he's been "irked" by Mulcair's comments about "Laurier Avenue," a reference to the staff at NDP headquarters in Ottawa. In recent debates Mulcair suggested the central office tried to exercise too much control in the Quebec campaigns.

"It was Laurier Avenue that won the seat for him, that put the resources into Quebec, that put organizers into Quebec that weren't there before," he said, adding that Mulcair, to a certain extent, has tried to take too much credit for the NDP's success in Quebec.

The party won 59 seats in the province last May, propelling it to Official Opposition for the first time in its history.

Broadbent, who helped launch Topp's campaign, bluntly agreed that he is concerned about the direction Mulcair would take the party.

"Yes, that's why I'm supporting Brian," he said, noting that Topp has a "deep commitment to social democracy."

"I think he clearly will take the party where I want to go, and he's shown that," he said.

Mulcair's campaign responded to Broadbent's comments with a statement that noted how much support he has from the NDP caucus.