I think pvr is referring to the rent-a-mob crowd who appear to turn up at every demo with their Socialist Worker Party placards and scarves around their faces. We used to call them "crusties" in my day. They've been out on the fringe for years because no sane party would ever entertain their policies but maybe now they've found a willing ear in Corbyn.
Does anyone else think this is effectively a Trade Union coup of the party? As if Labour are all of a sudden going to find hundreds of thousands of new members virtually overnight when they've just been thrashed at the last election with a leader who was already quite left leaning. There's a reason Corbyn and his ilk never made it as leader before. It's no coincidence that a Trade Union bill is about to go through parliament, finally putting an end to the farce of strikes where about 10% of the membership have voted 'yes'.
You can never discount anything in politics but I think Labour, unless something miraculous happens, are absolutely stuffed for a generation. They don't appeal to the mainstream electorate with their core beliefs any more. The world moves on and the comrades haven't.