If they could have extracted a genuine commitment to  proportional representation, it might have been defensible. But the vague promise of a referendum on a demonstrably crap version of pr, which the tories have promised to bitterly oppose, simply isn't good enough.

If they wiun the referendum and get changes to the election law they will have delivered systemic change that should increase their seats even if they loose votes.

If they loose, then right after the referendum would probably be the best time for the lib-dems to pull the plug on this government (and thus, I presume, trigger elections). If they need a reason they can always cite how mean the tories were in the campaign and find some promise tories reneged on.

Even with one of the crappier versions of pr, I would guess reform would get more votes then the libdem got in the last general election (if not, someone has not done their polling). When Tories and Labor congratulate each other on defeating the evils of equal representation is precisely the right moment for the libdems to try to rally those that just got voted down to "vote again for pr, and this time we will win!"

Played right, a general election coming on the heels of a referendum on the election systems, were tories and labor collaborated in the campaign, should give the libdems a fantastic opportunity.

This all assuming their will be a referendum.

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