Britain's Labour Party will name a new leader on September 12 following the resignation of Ed Miliband in the wake of his shock election defeat last week, the party's executive committee says.
Nominations will close on June 15, the party said on Wednesday.
The party's main spokespeople on business, Chuka Umunna, and on health, Liz Kendall, have already declared they will run for the post of leader.
Umunna, 36, would be the first ethnic minority leader of a major British political party but is seen by critics as too inexperienced, having been elected to parliament for the first time only in 2010.
In a video statement posted on Facebook Mr Umunna said he believed Labour could win the next election and that he wanted to create a "fairer, more equal society".