In March, the Parliamentary Labour Party voted for the Coalition government's benefits spending cap.

Not just any cap, or even the principle of a cap, but George Osborne's precise, £119.5 billion punitive limit covering most things save pensions and Jobseeker's Allowance. Only 13 Labour MPs refused to follow their leadership.

Ed Miliband took this course despite warnings from Save the Children and others that the £3bn in "savings" sought by Osborne would throw 345,000 children into poverty over the space of four years. Miliband also did not listen to campaigners who said that, once again, the disabled would be victimised. Labour's justification was that it would manage the cap with more "fairness" than Iain Duncan Smith. Such, these days, is the party's yardstick.

Obviously enough, even that achievement - if the word is deserved - would depend on Miliband winning a General Election. At the time of writing, YouGov's September polls have discovered Labour leads over the Conservatives of between 1% and 3%. That might do, just about, if you set aside the fact that two-thirds think the leader of the Opposition is doing "badly", and then forget that Miliband and Ed Balls are not rated highly - to put it gently - for economic competence. Miliband is in no position to guarantee fairness to anyone.

That hasn't stopped him, of course, from throwing the word around during one of his visits to Scotland. What else does he tell people who are deserting the Labour cause in the independence referendum argument? His party constitutes Better Together's last line of defence and the defence is crumbling. Precious few Tories would or could reject the Union that defines them. Labour people - if such a constituency still exists - need to believe that hope remains for social justice within the United Kingdom. So Miliband obliges.

The SNP, he tells us, is offering "a con". The fact that no-one will be voting for that particular party on September 18 is ignored, as ever. According to Miliband, "a Labour government is on the way, a Labour government with genuine proposals for social justice". That this would also be a Labour administration capitulating in the argument over austerity, one that will abide by Osborne's spending plans in all things, one that can provide only a sketch of "more powers" for Scotland, is also overlooked.

In this country, Miliband's colleagues like to accuse the Nationalists of failing to use such powers as they already have. The argument runs that more could be spent on childcare provision, for one example, without the fuss and bother of independence. Labour fail to state what should be cut - from a Scottish budget shrunken by Osborne - to make such things possible.

They are not keen, either, to explore Jack McConnell's recent assertion that the Barnett formula will give way to a "needs-based assessment" - assessed by whom? - if there is a No vote. How this could ever sustain anyone's dream of social justice is a question unanswered. Why a country perfectly capable of independence would submit, in any case, to means-testing by a government bent on cutting its budget is another of life's mysteries.

Run your own affairs or squabble with Balls over the nation's wealth? Compete for a slice of the loaf you baked in the name of solidarity? The benefit cap vote was a sure sign of Miliband's intent. If he is elected - that gigantic "if" - there will be plenty of talk of fairness to go around, but social justice will remain a cap-in-hand affair for every part of his UK. To Scottish Labour voters choosing Yes, that sounds like the Union they know only too well.

To them, Miliband offers a faintly comical proposition: vote No for the sake of his ambitions and all will be well. If ever a plan was fraught with risk, as Better Together would otherwise say, that one leads the field. Even if you make the bet that Labour can fend off Ukip, prevail against voting habits in the English south, suppress its own worst instincts and see sense amid the austerity mania, you are left with a question: When did Miliband's party last deserve to be called progressive?

A typical Labour answer might be, "It depends what you mean". The party's leader would point, as he did last week, to plans for a 50p income tax band and a 10p starting rate. He would assail the SNP, hypocritically, for planning to cut corporation tax after serving in government while Gordon Brown did that very thing and boasted about it. Miliband would offer a (temporary) freeze in energy bills and then grow vague when more powers for Holyrood were mentioned.

But still: that benefits cap. Real money taken away from real people simply because Osborne means to diminish the state and because Labour no longer has the Balls to say that this is economically stupid and morally wrong.

Nothing progressive can come from a party bent on such a course. Nothing that party offers, circumscribed by expediency and electoral calculation, matches the opportunity for Scotland of independence. You can have Miliband's remote hopes. Or you can rip it up and start again.

The fact raises another detail left unspoken by Labour's leader last week as he struggled to rally the troops and shore up a No vote: Nationalists themselves no longer pretend that the Yes campaign is their property. People, especially Labour people, insist noisily that their choice of independence has nothing to do with nationalism. This is fundamental.

These voters, these patient insurgents, are not interested in a Miliband policy auction. Worthless "guarantees" based on the theoretical possibility of yet another compromised Labour government no longer detain them. The point now is self-determination, not the SNP. If you want social justice in Scotland, design it yourself, argue for it, and vote for it. This is a DIY job; home assembly required.

Miliband has few choices in the matter, of course. He personifies all the contradictions of British Labour. His colleague Andy Burnham, who set in motion the process by which Hinchingbrooke hospital in Huntingdon became a privatised "operating franchise", now warns against the privatisation of NHS England. Good for him. So below the Border Labour campaigns against what was, barely five years ago, Labour policy.

No-one can force a Scottish government to privatise Scotland's NHS: that has never been argued. Edinburgh's budget can be squeezed, though, and there is plenty of appetite for that, as Lord McConnell has illustrated, in Westminster. But the Labour voters turning to Yes have a still deeper understanding of reality: judge London's parties by what they have done, by what the Tories are doing, and by what Miliband would do while he serenades us with fairness. Contracts to private firms from NHS England topped £10bn in 2013. Call it a clue.

"Trust me," says Miliband, "I'm progressive. I ache for justice and fairness. Just ignore all the things my party has done and means to do if another generation believes a word of it." In days of hope, the ambitions of this year's Labour leader seem like paltry things. Worse than that, they seem - because they are - all too familiar.