"Jeremy is a good man with great Labour values ... but he is not a leader who can lead us into an election and win for Labour,"
A second British Labour opposition lawmaker entered the contest to topple leader Jeremy Corbyn on Wednesday, boosting the veteran left-winger's chances of being re-elected by splitting the support of those who oppose him.
Labour is engulfed in a bitter internal power struggle between Corbyn's supporters in the grassroots membership and the party's lawmakers, who overwhelmingly rejected his leadership after Britain's vote to leave the EU last month.
Owen Smith, Corbyn's former work and pensions policy chief, said he had hoped the situation could be resolved without a "damaging, divisive contest" but despite three meetings with Corbyn, had failed to persuade him of an alernative route.
The leadership contest was triggered on Monday when lawmaker Angela Eagle challenged Corbyn. On Tuesday the party ruled he had the automatic right to stand in the contest without needing to be nominated by lawmakers.
"Jeremy is a good man with great Labour values ... but he is not a leader who can lead us into an election and win for Labour," Smith told BBC radio on Wednesday.
"I have a radical and credible set of policies. I want to put that to the membership, I want to make my case to be the next leader of not just the Labour Party but the next Labour prime minister."
Some lawmakers fear having two candidates run against Corbyn reduces the chances of ousting the leader, by splitting the support of those party members who want to see change.
If Corbyn, who was elected last September and retains strong support among the party's more left-leaning rank-and-file members, is re-elected in the contest, the party may split.
Smith said he did not want to split the party, and would stand by the result of the contest.
"I will be Labour until the day I die," he said.
"I will stand in this election and I will do a decent thing and fight Jeremy Corbyn on the issues ... and at the end of that I will stand behind whoever the leader is but I hope and I expect it will be me."