Derek Allen: Chewing the fat over ludicrous proposal to levy tax on chocolate

FOR a politician, the art of taxation is to pluck the goose with the minimum of hissing. And an elegant way of raising tax is to increase or introduce a levy on things that are deemed "bad" for us.

This provides governments with the chance to explain that the extra financial cost may be paid back in social or health benefits. It would be no surprise if proposals for "sin" taxes emerge in the coming years.

This year, I have heard proposals which, as a man who enjoys his comforts, send a shiver down my spine. Let's examine one in particular – a proposal to tax chocolate.

This was suggested by a GP and came about because of medical concerns about obesity. Tackling obesity is an important health policy outcome.

But achieving this outcome through taxation of specific products is wrong.

Taxing selected foodstuffs would be a very blunt instrument – expensive to collect, complex to introduce and would punish those least able to pay.

It could also start the state on the slippery slope of interfering with personal freedoms and choice.

Taxation works best when it is targeted. Here's a tongue-in-cheek look at how a targeted tax on obesity might work, but it illustrates why a "sin" tax often fails to address the problems it purports to address.

To tackle the problem behind the GP's proposal, we could introduce taxation based on people's weight, to address those deemed most "at risk". People with a Body Mass Index (BMI) of 25 or less could be tax-free.

A BMI of 25 to 30 (slightly overweight) would face a fat tax of 100 per person per year. This could easily raise an extra couple of billion a year. People with a BMI of 30 to 35 might face an annual tax of 500, and anyone heavier than this would face a punitive 1,000.

Taxation on this model is unrelated to the ability to pay, so a better model might be to vary the rate of tax on the individual's income.

Thin people might be taxed at rates, using 2011 as an illustration, of 20, 40, 50 and 61.5 per cent (yes, 61.5 per cent is the top marginal rate announced by Chancellor Alistair Darling for 2011), but larger people might face higher rates.

A formula of raising the tax rate by 1 per cent for each unit above a BMI of 25 has the potential to encourage self-regulation of weight. It is fairer than an across-the-board levy on a bar of chocolate because it addresses the circumstances of the individual taxpayer.

But could this be enforced and collected? Not a chance.

Tax evasion would be endemic. Such a tax would also possibly be a violation of human rights.

Think all this is ridiculous? It's not. Taxing our indulgences has never worked terribly well, whether the tax is indirect or direct. The UK imposes substantially higher alcohol duties than most of our European neighbours, yet we have comparatively high rates of alcoholism and binge drinking.

The same is true of tobacco. Compliant consumers would be outraged if they knew that the illicit market share of hand-rolled tobacco is estimated by HM Revenue & Customs at between 48 and 59 per cent.

For branded cigarettes, percentage is between 9 and 17 per cent, or between one in six and one in ten cigarettes smoked in the UK have no UK duty paid.

When politicians suggest "sin" taxes, they should be well advised to think it through carefully. Complacency could lead to the erosion of civil liberties, a poorer quality of life and criminality.

• Derek Allen is director of taxation at the Institute of Chartered Accountants of Scotland.