THE social justice secretary, Alex Neil, was the butt of much wry humour after his embarrassing “clarification” on tax credit cuts, hours after he said the Scottish Government was powerless to reverse them. But he should be congratulated.

A lot of poor people in Scotland are sleeping just a little easier this weekend because he decided to take it on the chin. He promised, however, belatedly, that low-income families “will have their lost income restored”.

This has been a very difficult week also for the broader independence movement, for whom support for the Scottish National Party was always conditional and not an act of blind faith. Nicola Sturgeon has been a brilliant advocate of policies like nuclear disarmament and has vigorously opposed Conservative welfare reforms while the UK Labour Party was equivocating upon them. But she is no longer alone.

A minor earthquake took place in Scottish politics last week as the Scottish Labour Party under Kezia Dugdale repositioned itself to the left of both UK Labour and the SNP. The immediate response from many nationalists – especially the virulent SNP partisans on the internet – has been to decry the change as insincere and devious. Red Tory lies.

Too many nationalists seem incapable of understanding that Labour Party members can be just as serious about opposing nuclear weapons as they are. Or that Kezia Dugdale cares as much about the impact of tax credit cuts as Nicola Sturgeon. This is infantile and demeaning.

Oppositions are there to oppose, challenge and hold governments to account – and effective opposition has been sorely lacking in Holyrood. Until last week. The Scottish Government had been holding the unsustainable line that it could do nothing to restore lost income to those families because it lacked the powers to change the tax credit legislation. This was always disingenuous.

I tweeted on Tuesday that, “Holyrood lacks the formal power to reverse tax credit cuts. But the Scottish Government certainly has power to compensate the victims. See bedroom tax.” This led to one of the most astonishing outpourings of offensive paranoia that I have experienced on social media.

I was denounced as a bought-and-sold apologist for the Labour Party, and called many unpleasant names including “traitor”. I now know how Jim Murphy felt. Even the more reasonable elements insisted it was impossible to restore tax credits in Scotland, and even anti-Scottish to try.

The very next day, the social justice secretary, Alex Neil, conceded that it was possible. This was was clearly a U-turn – but an honourable one. The internet clans then did their own handbrake turn and claimed that this had been the policy all along, and continued to denounce anyone who disagreed.

Of course, the SNP is not to blame for introducing tax credits in the first place. Nor will Holyrood have the full armoury of tax powers – National Insurance, Capital Gains, Corporation Tax – necessary to fully manage its own financial affairs. However, the fact that it does not have all tax powers doesn’t mean that it should not use the ones it does have or will have.

No-one forced the Scottish Government to sign the Smith proposals for income tax devolution. I said at the time it was a “transparent fiscal trap”: that the Tories intended to cut benefits and then give Holyrood the powers to reverse them through increasing taxes. This was all so that the Scottish Tories could relaunch themselves as the party of lower tax.

Well, the Scottish Government fell into the trap with its eyes open – presumably hoping it could simply ignore the new tax powers once they were in place. The truth is Holyrood has had income tax raising powers since 1999 and no party has ever used them.

What they didn't expect was that Kezia Dugdale would turn Scottish politics upside down by promising– effectively – to increase taxes in Scotland to reverse benefit cuts. No – she wasn't entirely clear how this would be paid for since not cutting Air Passenger Duty (APD) and not increasing tax thresholds does not of itself raise any new money. The cash still has to be found from somewhere.

But since the Scottish Government had evidently carved out a pot of cash to meet the cost of reducing APD it was not unreasonable of Dugdale to suggest that it could be used to help defray the £400m or so required to compensate the 250,000 families who lose out.

It's a question of priorities. By not increasing the threshold for higher-rate tax, those earning up to £50k would be paying up to £1,280 a year more than their counterparts in England.

Nationalists dismissed Kezia Dugdale for her “back-of-an-envelope” calculations. But at least she had an envelope with some numbers on it. Until last week the Scottish Government didn't have any numbers, and it still hasn’t explained what it will cut to pay for APD, let alone how it can now restore tax credit cuts as well. Raising taxes must be a possibility for all parties serious about this issue.

Yes, there has been fiscal sophistry on both sides. Nicola Sturgeon pointed out that Kezia Dugdale had “already spent” the APD money on education, during an interview with Holyrood magazine. She has a point. But the First Minister thus tacitly conceded that there was an opportunity cost in cutting APD that could be used to help restore tax credits.

There had been an uncomfortable silence on this since the finance secretary, John Swinney, at the SNP conference in Aberdeen, effectively ruled out restoring tax credit cuts on grounds of “affordability”. He said it was “highly unlikely” that the Scottish Government could find the cash to reverse them.

Well, now that Nicola Sturgeon has said she will restore this cash, there will be frantic activity in the bowels of St Andrews House as civil servants try to find savings elsewhere. It’s a safe bet that the Scottish Government is looking at manipulating tax thresholds too.

However, the immediate problem is that, as with APD, Holyrood doesn’t get the powers to vary rates and bands of income tax until 2017/18 at the earliest. The immediate problem is how to compensate families in the next two years.

Thanks to the House of Lords, the UK Chancellor has been told to go home and think again about the tax credit cuts and soften their impact. This should give the Scottish Government some financial wriggle room. But it is going to be desperately tight. The Scottish Government has already compensated bedroom tax losses and two years ago set up the £33m Welfare Fund for benefit claimants in distress.

John Swinney is right to say that they can't go on indefinitely restoring benefit cuts without damaging other areas like health, spending on which has been rising at a lesser rate that in England. But Nicola Sturgeon is also right to accept that the Scottish Government must help these families.

This might be the moment to take this issue out of the party political arena altogether. Nicola Sturgeon could agree with Labour that a means must be found to mitigate the impact of tax credit changes. Both parties could then invite the views of the people who really pay: the Scottish taxpayers, either through polling or perhaps even a referendum.

As a nation, we must stop kidding ourselves. If we want true social justice, we must prepared to pay for it by a modest increase in taxes.

Scotland has turned a corner this week. Now that an early referendum is off the agenda, we can see that tax is likely to be the dominant issue in Scottish politics for the next decade. This needs to be taken out of the poisonous arena of party politics.

The SNP is no longer the sole proprietor of the centre left. The vast majority of indyref supporters don't believe Kezia Dugdale to be spawn of the devil, and want to see some constructive engagement. Now is the time to set aside tribalism in Scottish politics.

If they can’t work together to help the poorest families, when will they?