It has been interesting to observe defeated SNP leadership contest candidate Kate Forbes question the Scottish Government’s income tax policy.

In its Budget in December, the Scottish Government announced rises in income tax for higher earners which will widen further cross-border differentials.

Ms Forbes is, of course, a former cabinet secretary for finance and the economy.

And her key policy views set out during the leadership contest last year seemed to land better with the business community than those from the victorious Humza Yousaf.

Furthermore, given the economy will likely always be a key area for debate when it comes to independence, SNP politicians and party members across the spectrum should probably listen to what Ms Forbes has to say.

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The Brexit brigade somehow managed to get by without making any coherent economic argument for the UK leaving the European Union. The electorate in the UK, although not in Scotland, of course backed this folly. In the case of Brexit, the economic cost was crystal clear for anyone who wanted to look, with the Tories ultimately opting for the most damaging form of departure.

In spite of the experience with Brexit, recent history has suggested that opposition politicians in Scotland will always make the biggest noise possible in demanding that politicians advocating independence lay out in great detail what it would mean for the economy.

Returning to Ms Forbes, to say that she is someone who should be listened to does not mean that there is not room for disagreement or at least debate around what she says.

Ms Forbes has, of course, had to deliver challenging Budgets herself. However, the numbers faced by Deputy First Minister and Cabinet Secretary for Finance Shona Robison in her December Budget looked particularly difficult to balance.

There is clearly room for debate about the degree to which Scotland should use its devolved powers on income tax.

And there have been moments when policy in this area has looked somewhat petty. These moments have generally been brought to us by the Scottish Greens, junior partners of the SNP at Holyrood, notably the refusal to move the higher rate threshold up in line with inflation at a time when this would have been the natural and fair thing to do. This was, of course, before the UK Government’s huge tax grab by way of freezing income tax thresholds for years.

It seems at times politicians favour real-terms tax rises by freezing thresholds - certainly the Conservatives have at Westminster. You sometimes wonder if this is because they think it is less likely to be noticed by the public.

That said, the Greens seemed to be making a point with their past refusal to edge the higher rate threshold up in line with inflation, a move which it must be said hit middle rather than higher earners.

Returning to the current situation, what did Ms Forbes have to say?

Writing in a Highland newsletter, the Mail on Sunday reported, Ms Forbes declared: “Continually increasing taxes is ultimately ¬counter-productive over the long term, even if you agree with it ideologically, because it ultimately reduces public revenue.

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“The forecasts for what the Scottish Government will raise through its latest changes to the top tax bands is just over £80 million. That isn’t to be sniffed at. But the forecasts also suggest that they’ll lose £118m that they could have raised because of behavioural change - people leaving or reducing their hours or treating their income differently. That illustrates that we need to invest in people, in job creation, and in better wages. That way the tax take will increase.”

The forecast of £118m comes from the Scottish Fiscal Commission, and relates to the reduced yield it sees from behavioural change in 2024/25.

Ms Forbes argued that, rather than taxing existing earners more, the best plan was to increase the number of people paying tax in the first place.

She said: “I’m constantly going on about the tax base. What I am really talking about is people. Calling for a bigger population, through inward migration and retaining our people, is exactly the same thing as wanting to see the tax base increase.”

The behavioural change point is an interesting one. The Scottish Fiscal Commission is obviously a very serious forecaster but only time will tell the degree and precise financial effect of behavioural change.

Looking more broadly at the greater income tax burden north of the Border, which derives in very large part from the huge difference between the higher rate threshold in Scotland and the rest of the UK, it is important when weighing the economic effects to consider where the money is spent.

And the Scottish Government does certainly look to have prioritised areas that will deliver an economic benefit as well as social good.

Free university tuition for people in Scotland is a fine example of this. If we want an economy which prospers from having a skilled workforce, propelled by high value-added activity, free university tuition is crucial. It enables far wider access to higher education, and avoids this opportunity being based on having money to pay fees rather than on ability.

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And free university tuition may well make it likely that more people in Scotland will ultimately stay here.

Similarly, the Scottish child payment from the SNP and Greens is putting money in the pockets of those who have to spend all or the vast bulk of what they have to live, thus bolstering aggregate demand and boosting businesses.

It is always frustrating to see people deal with, or think of, a country’s finances like a household budget. All too often, there is a focus on the cost line, and a message that there is not enough money for this, that or the other. Labour leader Sir Keir Starmer’s U-turn on his previous promise of free university tuition south of the Border is a good example of such dispiriting declarations.

The fact of the matter is that, if growth can be stimulated, tax receipts will be boosted and there will be more money to spend.

Ms Forbes’ observation about the importance of “a bigger population, through inward migration and retaining our people” to “see the tax base increase” is obviously very sensible indeed.

That is what will ultimately boost Scotland’s growth potential. The problem is that the UK’s hard Brexit has hammered net migration from European Economic Area countries.

So there are clearly challenges, not made in Scotland, to increasing the nation’s tax base.

We are likely to hear a lot more from Ms Forbes on the Scottish economy, and that is to be welcomed.

There certainly look to be good things from an economic and societal perspective, as well as some dangers perhaps, in the Scottish Government’s income tax policy.

It is a crucial issue, so healthy and informed debate is a good thing.