IAIN DUNCAN SMITH'S intervention in the independence debate was cack-handed to say the least. Popping up in Glasgow to make a speech in welfare, he made seemingly ill-informed comments on Scotland’s tax base before popping back down again to London.

Alex Salmond put the boot in. He torpedoed the tax / spend case against independence with some pithy statistics. He lambasted IDS as a typical Tory standard bearer for unionism – patronising and doing Scotland down. And he denounced the cruel Westminster plot to slash benefits to the needy in Scotland. He even used the row as leverage in his discussions with David Cameron on the terms of the referendum.

The UK government’s response? Deathly silence.

Four-nil to the nationalists.

But it was a game the government should have won. The truth is that the SNP doesn't have a leg to stand on when it comes to welfare. Social deprivation is Scotland’s most pressing problem. Rates of family breakdown, crime, worklessness, drug addiction, and life expectancy are appalling and inflict misery on up to a quarter of the population.

Moreover, the welfare bill in Scotland, in the context of free care for the elderly, an elderly population and a worsening picture of long term unemployment, will quickly become unaffordable without serious reform.

Meanwhile the principles of welfare reform – cutting back its excesses and improving incentives to work - are widely popular.

And yet, in all its years in power, the SNP has done nothing to help solve Scotland’s poverty problem, as John Swinney’s vapid budget last Thursday demonstrated. By contrast, Iain Duncan Smith has spent much of the last decade studying these issues, not least as they impact on society north of the border. His resulting policies, though controversial, have won strong support from across the political spectrum. He knows more about poverty in Scotland and how to tackle it than the entire SNP cabinet put together.

The government should be winning the argument on welfare in Scotland, just as it is at Westminster. So why was Salmond allowed to get away with his snatch and grab victory last week?

The problem is that the UK government is pathetically ill-equipped to deal with the SNP politically in Scotland. Time and again, on issues reserved to Westminster, the government is wrong-footed by the nationalists. On defence, Salmond gets away with his ludicrous hypocrisy about the Scottish army. On foreign policy, his evasions about EU integration and the Euro crisis go unchallenged.

It should be an open goal to contrast the Treasury’s plans to cut corporation tax with the Scottish Government’s ever more burdensome levies on business. Yet Salmond and his useful idiots in the Scottish business community are allowed to pretend that independent Scotland would have a more attractive tax regime than the UK.

These are issues that the cross party campaign Better Together cannot address. We can’t expect Labour figures like Alistair Darling to campaign in favour of government policy. And the Tory and Lib Dem rumps at Holyrood have neither the expertise nor the remit to take up the challenge.

Instead we need dedicated UK government spokesmen appearing all the time in the Scottish media to explain the government’s polices as they relate to Scotland and rebut the SNP when it attacks them. It’s not enough to claim that the government lacks sufficient junior ministers, or that Scotland on its own does not merit such attention. The independence issue should be the UK government’s most pressing priority. A ‘yes’ vote – even a close ‘no’ vote – would be a catastrophe for Britain and for any government that presided over it.

The campaign for Scotland in Britain needs to exist at three levels. At Holyrood, the opposition parties, particularly Labour, should expose the SNP’s do-nothing approach to devolved issues. Johann Lamont is showing promising signs of exploiting this open flank. Better Together is the right platform for putting the general economic and social case for the Union. The missing link is the UK government itself. Salmond finds it much too easy to criticise the Coalition, and this undermines the unionist cause as a whole, because he can put pressure on Labour to agree with his uncontested assertions. He wins both ways. If they agree with him about the evil Tories, they reinforce the case for separation. If they do not he can portray them as quislings.

The Secretary of State for Scotland, Michael Moore, is doing a decent job negotiating the terms of the referendum. He will not doubt play a useful general role in the campaign over the coming months. But he is not the man to go toe to toe on a daily basis on the details of coalition policy. The government needs a number of articulate, specialist figures to put its case, day in and day out. It’s no good ministers popping up and popping back again. That just leaves the SNP time to think, free to respond, and free to spin the issue as it sees fit without any opposition.

If you leave the field free to your opponents, they’ll win the battle.