Research by the Institute for Fiscal Studies (IFS) shows that despite this, and in contrast to the original SDIL, the effects of these changes on sugar consumption will be extremely small. The IFS estimates that the reforms will reduce average per-person calorie intake by 0.3 kcal per day (less than one five-thousandth of the recommended daily calorie intake for adults).

This is around 60 times smaller than the effect of the original SDIL, reflecting lower baseline sugar consumption from soft drinks compared with 2018, a smaller share of the market being brought into scope, and smaller expected reductions in sugar per product. Small effects on sugar intake also mean that the costs for families will be small, costing the average household less than 2p per week.

However, small effects do not in themselves make these reforms misguided, says the IFS. One advantage of the reforms is that they are expected to have larger effects for households who purchase the most sugar, who are most at risk of excess sugar consumption. But set against the government's claims that the changes will ‘protect children and improve health', these effects won't move the dial on sugar consumption or childhood obesity.

The reforms also do nothing to correct the underlying peculiarities that mean the sugar content of the heaviest-sugar drinks are taxed more lightly than lower-sugar alternatives. Taxing high-sugar products more heavily would reduce sugar consumption among the households that purchase the highest amounts of sugar in a more targeted way than the current system.

Other key findings from the new research include:  

• Producers and manufacturers were highly responsive to the original soft drinks levy, with many reformulating their drinks to sit just below the existing taxable threshold. Prior to the introduction of the SDIL, 2% of soft drinks sold had 4.5–5 g of sugar per 100 ml; this has now risen to 8% of the market. The recent changes will bring these drinks into scope of the tax.
• The reforms are somewhat targeted at households who purchase the greatest proportion of their calories from sugar: 14% of soft drinks bought by this high-sugar-consumption group will be affected, compared to 10% for the households with the lowest sugar intake. But even for this high-sugar-consumption group, the effects of the reforms will still be very small (cutting out 0.4 kcal of sugar per day).
• Increasing taxes on the highest-sugar drinks would be a better way to target the heaviest consumers of sugar. A 7p increase in the higher rate of the SDIL would have the same average effects on sugar intake as the actual reforms, but would reduce sugar intake by 0.6 kcal per day for the households that consume the most sugar.

Gautam Vyas, research economist and coauthor of the report, said: ‘A well-designed tax on soft drinks can be an effective way to improve diets – but the Soft Drinks Industry Levy gets the targeting backwards. Among in-scope products, sugar is taxed most lightly in the drinks that contain the most of it. The recent changes do nothing to fix this design flaw.

'A levy that taxed the most sugary drinks more heavily would be better aligned with the harms it is intended to address – and would do more to reduce sugar intake among the households who consume the most of it.'

Martin Brogaard, research economist and coauthor of the report, added: ‘These reforms are best thought of as small tweaks to the existing system rather than a significant step in tackling obesity.'