Sometimes a quick answer is the right one. Politicians hate to get boxed in and, as a result, often avoid giving straight and immediate answers to questions.

Sometimes this instinct is fine because the issue is one where a quick answer is unwise. Sometimes, however, dealing decisively with an issue right then and there is absolutely vital.

An obvious example of this is the request by Scotland’s Auditor General for the Scottish Government to give an order which will enable the Auditor General to obtain further information to help their scrutiny of the facts and circumstances surrounding the building of two ferries for CalMac. Lest we forget, these ferries are five years late and will cost three times their original budget.

These ferries are a scandal. A waste of money. A mess in which the Scottish Government is deeply implicated through its mishandling of the tender process, covert support for the Ferguson shipyard and the actions of the state-owned enterprise Cmal which commissioned the ships.

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The Scottish Government has been far from open throughout this long saga. To persuade the public that there has not been wrongdoing as well as incompetence there must be transparency.

If the Auditor General wants the Scottish Government’s assistance to get at the full facts it should get that assistance, rapidly and in full. The answer Yousaf should have given was a clear and immediate Yes.

Another example, potentially a more damaging one, is that Yousaf has not immediately ruled out a wealth tax when asked about how the increasing spending of the Scottish Government is going to be paid for. Yousaf probably doesn’t have the power to levy a wealth tax anyway, even if he could pretend it was local government taxation but let’s leave that issue for now.

There are two sensible principles when designing your tax system. First, you should tax flows of money and second, you should not narrow your tax base. A wealth tax goes against both of those principles.

Income Tax, National Insurance and Capital Gains Tax all take a share of a flow of your money. So does Inheritance Tax as assets flow from one generation to another. Even VAT attaches to a flow of money which you as the taxpayer can largely control the timing and extent of.

A wealth tax is a tax on something which is not a flow. You cannot just slice a corner off your house to pay it, nor until you have retired can you pay it from your pension. You have a tax liability but not necessarily the cash to pay it.

A wealth tax deliberately targets only a narrow proportion of the population. Those it targets are the very people we want to attract and retain in Scotland to drive our economy, create jobs and generate the tax revenues which pays for good public services. These people are highly mobile. They already pay a majority of the total income tax collected in Scotland. They don’t have to come to Scotland or to stay here. If the burden of tax on them is too great they will just base themselves elsewhere. Scotland’s loss will be England or America’s gain. This would be a self-inflicted wound of great stupidity.

The latest idea for a wealth tax in Scotland comes from a report by Landman Economics for the STUC. As you might expect the report is about raising money to invest in public services.

Unfortunately, as the report makes clear, its idea of “investment” is increasing public sector wages; which is actually spending rather than investment. In order to increase public sector pay it comes up with a cocktail of “progressive” tax measures of which a wealth tax is the one which will allegedly raise the most money.

The report has some errors in it such as claiming that the marginal rate of income tax is 42 per cent between £100,000 and £125,000 when in fact in Scotland it is already 62 per cent.

Helpfully, it has a table showing what the combined effects of its proposals are. This shows that the top 10 per cent of households by income will suffer a fall in their after tax income of 23 per cent, of which nearly all is caused by their proposed wealth tax because the tax on your wealth has to be paid from cash out of your income.

What do you think these households will do as a result of having nearly one quarter of their income wiped out? Sit and smile or up and leave?

A wealth tax would be a disaster for the amount of tax we raise in Scotland, it would damage our economy and reduce our ability to pay for public services. Other countries which have tried wealth taxes have quickly ditched them when it became blindingly obvious how counter-productive they were.

A wealth tax is a dangerous lemon of an idea. If he is any use Yousaf should rule it out right now as even the threat of it is damaging our economy.