David Miliband may be steaming ahead in the polls , but it's Brother Ed who's winning over the trade unions. A few minutes ago, the 1.3 million-strong Unison announced that it would be supporting him in the Labour leadership election.
Miliband has now won the backing of two of the "big three" unions (the GMB nominated him  last week), with only Unite left to declare. Ed Balls's team has long been hopeful of winning the Unite nomination, but Miliband has some significant backers in the union, including the joint general secretary, Derek Simpson, who anointed him as Labour's next leader in an interview  with the NS in March.
Since the abolition of the trade union block vote under John Smith, members have been free to vote as they wish, but in practice a significant number of Unison's members will back Miliband. In the 2007 deputy Labour leadership election, about 40-50 per cent of trade unionists voted for the candidate recommended by their union's leadership.
The unions have given Miliband's candidacy the momentum it needs: Ladbrokes immediately shortened the odds  on him becoming Labour leader. The challenge he now faces is to prove that he has popular appeal beyond his centre-left base.