The Bloc Québécois has now lost three of the four MPs who were elected under its banner in 2011, as the struggling sovereigntist party continues to lose ground on the federal stage.

André Bellavance, who was first elected in 2004, announced on Monday that he would now sit as an Independent and he would not run in the next election. At a news conference in his riding of Richmond-Arthabaska, Mr. Bellavance criticized the Bloc's new Leader, separatist hard-liner Mario Beaulieu, and lamented the infighting among sovereigntists.

"Mr. Beaulieu claims that he can rally people behind him, but in my view, that is far from being the case," Mr. Bellavance said. "There are MPs, presidents of riding associations and Bloc staffers who are leaving, and ex-MPs who are rethinking their plans of being candidates for the party in the next election."

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Mr. Bellavance finished second to Mr. Beaulieu in last June's leadership race, and he has never warmed to the rookie leader's plans to focus all of his energy on the promotion of Quebec independence. Traditionally, the Bloc played second fiddle to the provincial Parti Québécois when it came to pushing for sovereignty, and focused its attention on defending "Quebec's interests in Ottawa."

Best known for his fight to protect the French language in Montreal, Mr. Beaulieu did not seem to mind the departure, despite repeated entreaties to keep Mr. Bellavance in caucus.

"Those who are giving up will no longer stand in our way," Mr. Beaulieu said in a statement.

Mr. Beaulieu does not have a seat in the House, but is expected to run in a riding in the east end of Montreal next year.

"I knew from the start that things would not be easy," Mr. Beaulieu said. "Today, the road is even steeper, but to believe that we will not make it would be to underestimate the resilience and determination of the independence movement."

Once the dominant federal party in Quebec, the Bloc lost almost all of its seats in the 2011 election to the NDP's "Orange Wave."

The Bloc now has only two MPs in the House: Louis Plamondon, a party veteran who is the dean of the House of Commons, and Claude Patry, who was elected as a New Democrat and will not run again.

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Earlier this month, MP Jean-François Fortin quit the Bloc to sit as an Independent, expressing his disagreement with Mr. Beaulieu's approach.

"The Bloc Québécois in which I believed, in which we believed, no longer exists," Mr. Fortin said in a statement. "The arrival of new leader Mario Beaulieu, who is pushing a one-dimensional, unrigorous and uncompromising approach, has put an end to the credibility established by Gilles Duceppe and continued by Daniel Paillé, two leaders who deserved great respect."

The other MP who was elected under the Bloc banner in 2011, Maria Mourani, was kicked out of the party last year after she criticized the PQ's proposed "charter of values." She is also sitting as an Independent.

At his news conference, Mr. Bellavance said the sovereigntist family was increasingly divided, blaming the supporters of Mr. Beaulieu who have attacked him for his allegedly lacklustre support for Quebec independence.

"We shouldn't be washing our dirty laundry in public," Mr. Bellavance said, referring to a "witch hunt" inside the party.