How important are the trade unions in the Labour leadership contest?

Politics Explained: Union leaders play a key role in endorsing candidates, but it is members that have a much bigger say

The race to succeed Jeremy Corbyn as Labour leader is already well under way, despite the contest not officially beginning until early next year.

Behind the scenes, potential candidates are holding hushed conversations with Labour MPs, campaign teams are being assembled, funding secured, and alliances struck.

One of the key challenges facing the prospective candidates is winning the support of the 12 trade unions affiliated to Labour and, more importantly, that of their members.