The quiet man of politics has finally roared. Iain Duncan Smith’s resignation last Friday may have taken people by surprise, but in reality it’s no surprise at all.  The relationship between IDS and the Chancellor has, at best, always been tense. Their dislike for each other is an open secret, and IDS’s direct and almost disdainful public criticisms of the Prime Minister actually made it almost inevitable that he would have to resign at some point.  He’s been far more vocal in his criticisms of the Prime Minister than any of his other five Cabinet colleagues who are backing the Brexit campaign – with the possible exception of Boris Johnson.

Given that the Prime Minister had released ministers from the normal obligations of collective Cabinet responsibility over the EU referendum, it’s almost as if IDS was really only looking for another plausible policy reason to resign. Indeed, he had made clear just a couple of weeks ago that he was prepared to forego his Cabinet position if he was pushed to do so, and the Chancellor’s announcement on cuts to disability benefits in the Budget provided him with that reason.  IDS claims that his resignation was on the benefits issue and had nothing to do with the EU referendum.  In which case why did he not resign on Wednesday evening or Thursday morning – instead leaving it to Friday afternoon?

This has blown the rifts within the Conservative Party wide open.  With more and more backbench MPs coming out against the Chancellor’s cuts to disability benefits, forcing the Chancellor into a retreat on the measure saying that it would now be reviewed, there is more than a slight sense of this Budget going the same way as his “Omnishambles” Budget in 2012, or even worse. There can be little doubt that the gloss has already come off what was meant to be a Budget to steady the ship as the economic storm clouds gather.

But it’s the tone of IDS’s resignation that is so eye catching.  His resignation letter to the Prime Minister was openly critical of both the Prime Minister himself and the Chancellor.  The Prime Minister’s response was equally critical of IDS. There is a slight whiff of IDS trying to emulate Geoffrey Howe’s resignation from Margaret Thatcher’s government in 1990, and there is every reason to believe that this is not the end of the matter.  The respective “Remain” and “Leave” campaigns are now likely to become even more hostile towards each other. IDS’s resignation has blown apart any semblance of respect that the two camps may have been trying to preserve. The Conservative Party is in real danger of open civil war.

There had been much talk of both sides of the campaign coming back together on 24th June and carrying on as if nothing had happened. That now looks increasingly difficult. There has been open talk of a leadership challenge whatever the outcome and that too now looks a distinct possibility unless the Prime Minister wins the referendum by a comfortable margin.  But if it is a very close result, or if the outcome is to leave the EU, the Prime Minister’s future looks increasingly vulnerable – and so too does the Chancellor’s. They will live or die together.

Iain Duncan Smith’s resignation has lit the fuse.  What happens after June 23rd is now anybody’s guess. The euphoria and warm glow in those heady days of May last year when the Prime Minister pulled off a stunning election victory, delivering a Conservative majority for the first time since 1992, are a distant memory.