The Labour leadership race has gained further momentum today after Chuka Umunna became the second candidate to formally declare (following Liz Kendall) and Stella Creasy and Ben Bradshaw emerged as the latest contenders for the deputy post. The NEC will meet tomorrow to agree a timetable for the election (Harriet Harman outlined the three main options at last night's PLP meeting).

Ahead of MPs' nominations opening, sources tell me that the left of the party is also hoping to get a candidate on the ballot paper. Andy Burnham, who will soon launch his campaign, is regarded as insufficiently radical to be given a free run. The two leading contenders are Jon Trickett, the deputy chair of the party, who was yesterday reappointed to the shadow cabinet as shadow minister without portfolio, and Ian Lavery, the former NUM president and the chair of the parliamentary Trade Union Group. John McDonnell, the chair of the Socialist Campaign Group, who stood in 2007 and 2010 (but failed to make the ballot) ruled himself out of contention before the election. "I’ve done it enough times and been blocked from getting on the paper. How many times can I be hit by that?" he told me in March.

The challenge for whoever goes forward will similarly be to make the ballot. Candidates require the support of at least 15 per cent of Labour's 232 MPs (up from 12.5 per cent in 2010). But sources are hopeful that the arrival of more left-wing MPs at parliament (Cat Smith, Clive Lewis, Richard Burgon, Louise Haigh among them) will make the task easier. An alternative would be to appeal to other candidates to "lend" some of their supporters (as in the case of David Miliband and Diane Abbott) to ensure a full debate. While unlikely to win, a left-leaning candidate would have the opportunity to influence the eventual victor's programme and to represent a growing wing of the party.