The study, published in the Lancet journal, modelled different ways that the soft drinks industry could respond to the tax and then estimated what the likely impact would be on the health of the UK population. It closely follows the publication of draft legislation on the soft drinks industry level, published by HM Revenue & Customs (December 2016).

It predicted if sugar was cut in the sweetest drinks in response to the tax, levels of tooth decay, obesity and type 2 diabetes would fall, particularly among the high-consumption under-18s. Researchers said the overall effect of the tax - due to start in April 2018 - would be modest but significant. The tax will be applied depending on the sugar content of drinks, so there will be no tax on diet drinks, a lower tax on mid-sugar drinks and a higher tax on high-sugar drinks.

Professor Susan Jebb, study co-author at the University of Oxford, said: ‘In spite of the uncertainties, the direction of the effect is clear; this levy will have a positive impact, especially on children’s health. Of course, on its own a soft drinks levy cannot solve the obesity crisis, but we should not underestimate the importance of this step, both for the UK and as a case study for other parts of the world. Then, once this Bill is passed, we need to consider how to take effective action to reduce other sources of sugar in children’s diets, notably confectionery, which has so far been relatively overlooked while hearts and minds have been focused on the soft drink levy.’

Responding to soft drinks draft report, Dr Max Davie, Assistant Officer for Health Promotion for the Royal College of Paediatrics and Child Health (RCPCH), said: ‘After years of campaigning we are very pleased to see Government moving forward with this draft legislation.

‘The sugary drinks that will be affected by this tax have no nutritional benefit and often contain levels of sugar that are above a child’s daily recommended limit. These drinks are a major contributor to the high sugar intakes of children, particularly teenagers, and we are in no doubt that they are, in part, contributing to this country’s obesity crisis.

‘We hope that drinks manufacturers use the draft legislation as a spring board to show their commitment to improve child health and voluntarily reformulate their sugar sweetened soft drinks ahead of the policy passing into law. By doing so they will help thousands of vulnerable children and young people and will be going some way to protecting the future health of our nation.’

The Office for Budget Responsibility estimates the levy could add 18p to 24p to the price of a litre of fizzy drink if the full cost is passed on to the consumer. This amounts to an extra 6p on a regular can of Fanta and Sprite, and an extra 8p on a regular can of Coca-Cola, Pepsi and Irn-Bru.

However soft drinks firms say there is no evidence a tax would cut obesity. Gavin Partington, director general of The British Soft Drinks Association, said ‘The problem with this modelling is that it is based on the flawed concept that obesity can simply be attributed to calorie or sugar intake per se and consumption of one product in particular, rather than overall lifestyle and diet. This error is plain to see given that sugar intake from soft drinks has been declining for several years now, down 17% since 2012.’

Both reports can be viewed here and