Charles Moore succeeds in his Daily Telegraph column today in simultaneously scragging George Osborne while also supporting the Government’s proposed changes to the Personal Independence Payment, PIP.  Moore argues succintly that PIP works on a points system for aids and appliances; that the courts have widened the definition of these to the point where “someone who has to sit on a bed to put on his socks is now legally empowered to claim the bed as an appliance”; that this has contributed to the tripling of the number of aids and appliances claimed in 18 months, and that more “control has to be exercised” or “that way lies ruin”.

Iain Duncan Smith presumably agrees, since he issued plans last Friday for the reform of PIP – which is paid to people of working age.  It was these proposals which the Chancellor cited during his Budget speech, carefully referencing Duncan Smith’s publication of them.  Downing Street is already briefing that it is a nonsense for Duncan Smith to resign in protest against proposals which he himself promoted, and which will be watered-down anyway.

In a narrow sense, this is right.  But in a broader one, it misses the point – a massive one which has been gathering for years like a great stormcloud, has been growling and rumbling ominously away, and has now burst into the thunder and lightning of Duncan Smith’s spectacular departure.  ConservativeHome has long warned about it.  Duncan Smith’s resignation letter references it – indeed, puts it right at the centre of his reason for quitting.  “Too often my team and I have been pressured in the immediate run-up to a Budget…to deliver yet more reductions to the working age benefit bill,” he writes.

In other words, there is only so much protection of older richer retired people at the expense of younger poorer working ones that social justice can bear.  We have long made exactly this case, suggesting that the winter fuel allowance, free bus passes, free TV licences, the triple locking of pensions and the ring-fencing of NHS spending are now a hook on which the Government is impaled and from which it needs an Affordability Commission to wriggle free.

Duncan Smith’s letter goes on to make a further charge.  The PIP proposals, he writes, “are not defensible in the way they were placed within a Budget that benefits higher earning taxpayers”.  He is thus suggesting today what we wrote two days ago in the Budget’s aftermath – namely, that the income tax cuts it contained had less to do with sustaining recovery (let alone hitting Osborne’s own surplus target) than creating a feelgood factor for the EU referendum.  “Certain policies,” he adds, “…are more and more perceived as distinctly political rather than in the national economic interest.”  This is a brimstone missile aimed directly at the Chancellor’s character and conduct.

The response from Downing Street will be that Duncan Smith’s resignation is really all about the EU referendum – that even the freedom to campaign as he wishes was not enough to satisfy his passion for Brexit.  It is doubtless true that the Prime Minister’s propagandising for Remain, which at times has cut corners when it comes to the truth, has angered Duncan Smith.  But this resignation looks to be less about Europe than about social justice.

Duncan Smith’s appointment was risky from the first.  His relationship with Osborne went wrong very quickly.  David Cameron tried to move him from Work and Pensions to Justice, but Duncan Smith stood his ground and dug in.  Paradoxically, this man of the Right has looked lonelier in Cabinet since the Liberal Democrats left it.  So unhelpful to Gove over schools, they were often sympathetic to Duncan Smith over welfare, agreeing that too much was being asked of poorer working people and too little of richer retired ones.  But however different they may be in many respects, the two men are alike in one.  They have both been reforming giants – twin stars of that last Government.

This zinger of a resignation is an even bigger event, in terms of its implications for the Conservative Party, than Boris Johnson coming out for Brexit.  Boris was careful to praise the character of Cameron.  Duncan Smith has damned, more or less explicitly, that of Osborne – and, by extension, held the Prime Minister responsible for backing up his Chancellor.  The unity of the Party is already under strain.  Duncan Smith’s walkout makes it less likely that it will hold together after the referendum.  If Britain votes to leave the EU, I suspect he will be back in government immediately.  If it votes to stay, he will be a haunting presence, a rallying-point for protest – and, not least, a voice for social justice.  The quiet man has roared, and the echo is reverberating.  It may start an avalanche.