Well, I'm all for building effective extra-parliamentary support for an alternative to austerity beyond the ranks of Labour - but I simply don't think that the conditions exist at present for an alternative left party to make a UKIP style breakthrough.
I didn't happen to say a party necessarily had to do it
("UKIP have shown the politics of party X can be dragged in a given direction far better from outside than pushed from inside.")
In the case of "left of labour" I think you are right. The conditions don't exist (thanks to generations of naval gazing, fetishised rhetoric, sectarianism and one up-ship that has utterly fucked things in that regard)
What I suggest is that a broad movement can and should scare almighty fuck out of the government with concerted confrontation / civil disobedience etc. I wouldn't expect the Labour Party on board per se. Far from it, though many activists might be.
This is workable and it's important because
1) Most people can not change who the next government is, only a small number of swing voters in a small number of seats. We can argue for ever about who we should vote for but when it comes down to who has most seats at Westminster it's almost certainly an academic question in most cases.
2) Who ever forms the next government will behave better if we stand up to them, though we will need our narrative straight and plenty of seeming neutrals to be quite sympathetic. This is what gets me out of the "you're only ultimately working for Labour" bind.
The next government will be dominated by Labour or Tory anyway (no one ever seems to consider the mathematically sensible option of a Lab/Con coalition - not so much a policy issue, more that it would give the game away).
The point is to stand up to these psychopaths and criminals now.
3) If we don't kick up a big stink as a collective now then other anti establishment stinks could kick off and we will have missed the boat. Again. These could be reactionary, somewhat aimless or something else. But for the broad left not to take a united and confrontational stand at a time like this is actually letting a lot of people down anyway.