Unison, one of Britain's largest trade unions with 1.3 million members, has joined Unite in endorsing Jeremy Corbyn for Labour leader.

In a statement this afternoon, the union's general secretary Dave Prentis praised Corbyn's anti-austerity message:

Jeremy Corbyn’s message has resonated with public sector workers who have suffered years of pay freezes, redundancies with too many having to work more for less.



They have been penalised for too long by a government that keeps on taking more and more from them. Their choice shows a clear need for change towards a fairer society where work is fairly rewarded, and where those living and working in poverty supported.



Today’s decision is a recommendation and our members are of course free to cast their vote as to who they think should lead the Labour Party.”

The Sun's deputy political editor Steve Hawkes has called the move a "huge development", tweeting that Yvette Cooper's campaign "will be stunned".

Stunning. Unison union endorses Jeremy Corbyn. Huge development. Yvette Cooper's camp will be stunned. — steve hawkes (@steve_hawkes) July 29, 2015

Daily Mirror associate editor and New Statesman contributor Kevin Maguire also suggests that Andy Burnham would have initially expected the union's backing:

Unison going Corbyn 1 then Cooper 2 in Lab race another blow for Burnham who at campaign's start expected the union's backing — Kevin Maguire (@Kevin_Maguire) July 29, 2015

28,000 of Unison's members are also members of the Labour Party, and 15,000 are registered to vote in the leadership contest.

This morning, a poll leaked to the Mirror showed Corbyn with an almost 20 point lead over his nearest rival, Yvette Cooper.

Now read Stephen Bush on why he's convinced Corbyn will win.