This is a tricky faultline for the coalition – and not just because, speaking at a conference yesterday, Cable also suggested that it has forced him to "the limit of collective responsibility." Truth is, some Tories, both inside and outside the coalition, are sympathetic to the Business Secretary's position. Whether this weight of opinion will cause the government to dilute its immigration cap, I'm not sure. After all, even Cable is stressing that he's basically ok with the permanent cap that is being introduced next year – it's really the stop-gap version, in place now, that he has qualms about. But, in any case, this is a story that could cause equal parts embarrassment and strife for the coalition.
The question now is how all this will translate to the Lib Dem conference. There's little doubting that Cable is uniquely well-placed to stir up party sentiment against the coalition and its policies. If he decides to pack his verbal tommy gun for Liverpool, then there could well be blood.