Ed Miliband has won the backing of Britain's second biggest union, Unison, in his campaign to become the next leader of the Labour Party.
Yesterday's decision suggests that the younger of the Miliband brothers is emerging as the favourite candidate of trade activists, which will boost his vote but will be used against him by the Tories if he wins.
More than half a million Unison members can vote in the leadership contest, because they pay a £3-a-year levy to the Labour Party along with their union subscriptions. As their ballot papers are sent through the post, they will also receive mail from their union explaining why the union is recommending Ed Miliband.
The nomination comes amid a rumour swirling around Westminster that the heads of the three biggest unions – Unison, Unite, and the GMB general union – and of the smaller postal workers union, the CWU, met last week to see if they could all back the same candidate, but could not decide among themselves whether they preferred Ed Miliband, the shadow Energy Secretary, or Ed Balls, the shadow Education Secretary.
The next day, the GMB nominated Mr Miliband, while the CWU backed Mr Balls. Unison's decision to back Ed Miliband was taken yesterday by a committee of union members.
But a Unison spokeswoman said: "This story about the general secretaries meeting is a complete rumour. Meetings go on all the time.
"The only body that can recommend a candidate is the political committee. The recommendation is done through the union's democratic processes."
Between them, the four unions have around 2.2 million members who have the right to vote in a Labour leadership contest, but the days when union bosses voted on behalf of their members ended nearly 20 years ago.
Members vote by postal ballot and do not have to follow the advice given by their union. This year, the Labour Party's Procedures Committee has tightened the rules, to end the practice under which union members would get a ballot paper and advice on which candidate to vote all in one package. Unions have been told that they may advise their members on how to vote, but must do so in a separate mailing.
Ed Miliband said: "I am honoured and delighted to have received the support of Unison.
"Unison has gone through a thoughtful and thorough process of consultation with their members. To have received the backing of a union representing millions of frontline workers is a real boost for my campaign."
The country's biggest trade union, Unite, will decide on Monday whom to nominate, and is expected to back either Mr Balls or Ed Miliband. Unite has about 950,000 members who can vote in Labour leadership elections, compared with 576,000 in the GMB, about 500,000 in Unison and 180,000 in the CWU.
David Miliband has received backing from two unions – the shopworkers' union, Usdaw, which is Britain's fourth-biggest union, with 368,000 eligible members, and the metal and textile workers' union, Community, with 23,000. Diane Abbott has been nominated by the rail union, Aslef, with 16,000 eligible members. The other candidate, Andy Burnham, is yet to receive any union nominations.