AS he faced the media after his Commission's report was published on Thursday, Lord Smith of Kelvin wisely downplayed his own role, and left it to the politicians to explain the content.

"I'm just Santa's little helper," he smiled. But the Smith report is not only for Christmas.

This is not because the process of translating it into law will require months of debate at Westminster after a highly unpredictable General Election next May, nor simply because putting that law into effect is expected to take several more years. (As Smith himself noted, many of the key changes in the 2012 Scotland Act, which emerged from the Calman Commission, will take four years to bite.) No, the main reason we are likely to be talking about the Smith Commission for many a festive season yet to come is that it cannot last.

It is not a satisfactory or stable arrangement. It nibbled the constitution rather than reordering it, devolving powers in fractions - a slice of tax here, a crumb of welfare there.

Small wonder that Smith made it clear he was off to pastures new as soon as his report emerged. He did not want to stick around for the sequel.

In the strictest terms, the Smith Commission did deliver on the text of the famous "vow" made by the Unionist party leaders towards the end of the independence referendum campaign.

But only because the vow, as signed by David Cameron, Nick Clegg and Ed Miliband, was a deliberately vague pitch to the electorate.

It committed the three parties to making the Scottish Parliament permanent (in theory, but not in practice - it could be arbitrarily abolished by Westminster); said the Barnett funding formula would continue to inform Scotland's budget; and promised "extensive new powers" for Holyrood.

These new powers were never listed, and "extensive" in this context was never defined.

Much grander claims were made outwith the vow, notably the federal rumblings of Gordon Brown, but in its own terms the vow was met - although essentially because it cannot be disproved. Unionists may cheer, but it is hardly a triumph.

There are good points to the Smith Commission report.

Giving 16 and 17-year-olds the right to vote on the back of the referendum is a clear gain. And transferring some control over tax and welfare could prove to be better than none. But overall it is toe-in-the-water stuff.

Compare it to the areas passed to the Scottish Parliament at the outset of devolution: health, education, justice, the environment.

These have worked because they were areas devolved wholesale, not in slices or fractions.

Smith ignores that all-too-obvious point. Income tax is devolved in part, but not in whole, while the vast bulk of taxes remain reserved.

If an economic shock depressed income tax receipts, to which other taxes could a future Scottish Government turn to make up for it? It is like playing golf with one club.

Even former Labour first minister Lord McConnell warned on Friday that "in the longer term, everybody involved may come to regret putting all the eggs in the income tax basket rather than looking at a spread of taxes".

Likewise welfare, where a small number of benefits now come to Holyrood, but the majority remain the preserve of Whitehall.

No-one needs reminded of how tangled the UK's tax and welfare systems are - and devolving bits and pieces will only make that worse, and prevent Holyrood from at long last simplifying them.

Complex in their own right, tax and welfare are also intricately connected parts of the economy and central to any nation's political debate. They are an ecosystem; we got a potted plant.

As this newspaper reveals today, the Unionists in the Smith Commission could have delivered a rounder deal but lopped out powers in the closing stages.

Their inevitable comeuppance will be to go through a similar process in a few years' time.

The Smith Commission report is too scrappy and contains too many internal contradictions to endure.

But there is a bigger reason it is a stop-gap. As the polls show - including another published today - it is fundamentally out of kilter with public opinion.

The majority of people in Scotland want more, much more, than this and so they will keep voting for the politicians they feel can best deliver it.

If the Westminster parties think that, with the Smith Commission report, this clamour will all be over by Christmas, they should think again. The General Election looks as harsh as winter for them.