The man the right-wing press are calling 'Red' Ed Miliband has won the Labour leadership election, beating his more-Blairite brother David to the top job. The media are painting this as the 'death of New Labour' and the unions 'taking back' the Labour Party. Neither of these things are true (and there's nothing really 'red' about Ed Miliband's politics) but the fact that the media is portraying things in this way is significant.
Miliband's first speech contained plenty of criticism of 'irresponsible and reckless strikes' and was incoherent on many issues. But he did make some anti-cuts posturing and express some pro-union sentiments that would've been unimaginable from the mouths of Blair or Brown. He was elected by union votes and obviously feels under some pressure; we should help increase that pressure and try to make some of it tell, even if we're sober in our assessment of how likely that is.
RMT was expelled from the Labour Party in 2004, but ASLEF and TSSA are still affiliated. Whether affiliated or not, all three union should try to assert pressure on the leadership and direction of the Labour Party, putting maximum pressure on Labour politicians not to enact policies that attack the movement which founded their party. ASLEF and TSSA can use their affiliation to do that; RMT can demand commitments from its parliamentary group (made up entirely of Labour MPs) not to vote for any cuts policies, and pressuring Labour councils at a local level to defy Tory cuts.
Ed Miliband's election will not magically turn the Labour Party into an adequate working-class party, but it might create some openings.