As those of you who remember my writing on the subject will know, I’m no fan of the idea of a sugar tax.

But in making their case for one this morning, the members of the Health Select Committee seem to have stumbled on a good idea.

Not the tax itself, of course, but the use of sunset clauses.

The Committee are aware that one of the best arguments against a tax on sugar, setting aside raw principle, is that it risks joining the other so-called ‘sin taxes’ as a deeply regressive revenue tax on the poor.

Demand for things like cigarettes, and to a lesser extent alcohol, isn’t particularly price sensitive. This means that punitive tax rates don’t do much, if anything, to reduce consumption.

They do, however, take an increasingly large bite out of the disposable income of the least well off, a fact whose quality of life implications far outweigh their negligible impact on health.

Yet the Government continues to increase them. Why? Because they are reliable revenue raisers, sanctified by the puritanism of the age. Nobody’s going to criticise a Chancellor for giving smokers a kicking, regardless of whether said kicking actually does anything about their smoking.

So the Health Select Committee have proposed that their sugar tax, which will be set at 20 per cent, should be subject to a sunset clause.

A sunset clause is a provision in a piece of legislation that means that a law ceases to take effect after a certain period of time unless further, pro-active action is taken to extend it.

The Committee proposes that their tax should cease to operate if it doesn’t reduce levels of sugar consumption.

(Hopefully they are at least open to argument that it should be scrapped if consumption is not reduced sufficiently to outweigh the negative impact of the tax on quality of life in other areas.)

This is, at least in theory, a very good idea. The concept of a sunset clause, which allows policies to be tested before becoming permanent laws, is a feature much needed in British law-making, where repealing is rare, inertia is enormous and anything that gets on the statute book tends to stay there.

One example of where a sunset clause ought to have been used is the Fixed Term Parliaments Act, which could have been constructed to fall after a single five-year Parliament.

This would have given the Coalition the security it needed, and the option to fix the term of the next Parliament, without threatening to permanently introduce an unheralded and un-asked for change to our constitution.

However, there are reasons to be sceptical of how effective the Committee’s proposal would actually be.

After all, if a Chancellor could get such a law established as part of everyday life without losing office, they might simply find another handsome source of income on the Government’s books and be reluctant to relinquish it.

An unprincipled retention of a malfunctioning sugar tax – against the best intentions of the Health Committee, no doubt – wouldn’t be especially difficult, robed as it could be in high words about the war on obesity and saving little children.

There’s also the tricky fact that only the most commendably liberal of Chancellors is likely to risk setting a precedent that we should scrap sin taxes that don’t fulfil their notional goal of tackling consumption, lest people start asking awkward questions about tobacco duty.

Sunset clauses are excellent legislative practice. But they aren’t a magic bullet: without a will to repeal bad law and a more sceptical approach to public health legislation, they won’t operate properly.