By historic standards, the Labour left has been remarkable by its quiescence in this parliament. The anticipated split over austerity, as Ed Miliband and Ed Balls committed to strict deficit reduction targets, never materialised (in contrast to that of the Conservatives over the EU). But, apropos of nothing, 16 MPs from the party's left have just released a statement demanding a change of policy direction in three areas.

The first is over public spending. They reject Labour's pledge to eliminate the current deficit by the end of the next parliament, calling for a £30bn investment package funded either by higher borrowing, the state-owned banks, a new round of quantitative easing, or a special levy on the super-rich. The second is over rail policy. Rather than Labour's plan to allow not-for-profit firms to bid for franchises as they expire, the MPs demand that contracts are automatically returned to public ownership. The third is over trade union and employment rights. The MPs call for the promotion of sectoral collective bargaining and improved recognition for unions.

None of these demands are particularly original or surprising. But it is striking that the MPs (largely represented by the Socialist Campaign Group) have chosen this moment to apply pressure to Miliband. Many on the left believe that they can take advantage of the rise of the anti-austerity Greens and the SNP to push Labour in a more radical direction. In the likely absence of a majority, backbenchers such as the 16 signatories could exert significant influence over a minority or coalition government, determining whether it lives or dies. Just as the rebellions of the Conservative right, and David Cameron's subsequent concessions, have been a feature of this parliament, so those of the the Labour left could be a feature of the next.

Alternatively, should Labour lose, shadow cabinet ministers fear that whoever succeeded Miliband would struggle to avoid a major split (particularly were a "Blairite" candidate elected). Len McCluskey's repeated threat, both in public and in private, to establish a new workers' party if Labour is defeated is one that all sides are taking seriously.

Here's the statement in full.