The idea of a cross-party progressive movement against a hard Brexit is an important one, but it might be a mistake to present it as a short-term answer to the question of a Corbynite election strategy. Starting off with debates around electoral pacts and PR, pushes it straight into the arena where’s partisan interests are strongest.
Surely, it’s better to keep the focus on policies where common interests are strongest. One, maybe old-fashioned, model might be a platform like Charter 88, bringing together multiple parties with organised civil society institutions, unions etc, as well as stigmergic networks.
The role of those institutions would be to give the coalition sufficient heft to ensure that the various opposition parties voted together enough to exploit any cracks in the Tory majority. In effect, we need an extra-parliamentary movement for a parliamentary opposition.
As much as we shouldn’t fetishize Westminster, Tory hegemony may actually be weaker there than in the media. Indeed, Osborne’s strength may have been in using the latter to bolster the former, cultivating the lobby to psych the PLP about legislative ‘traps’.
A few Government defeats might improve morale across the board and open up space for larger discussions. This maybe assumes that there won’t be an early election, but it’s hard to see an electoral alliance being negotiatied ahead of an autumn poll, in any case.