Health advisers for Mayor of London Boris Johnson have swung their weight behind calls for a tax on sugary drinks, after new figures claimed the introduction could save London boroughs alone nearly £40m in costs to the NHS.

A report commissioned by the Children’s Food Campaign, in association with University of Liverpool academic Brendan Collins and FoodActive, claimed the measures would reduce the cases of diabetes by over 6,300, prevent over 1,100 cases of cancer and reduce strokes and cases of coronary heart disease by over 4,300.

Rosie Boycott, chair of the London Food Board, which is pursuing a five-year strategy on behalf of Johnson to tackle obesity, backed by supermarkets including Tesco, Sainsbury’s and Morrisons, welcomed plans for the tax.

“Sweetened fizzy drinks offer nothing to a city already suffering high levels of obesity-related diseases and dental decay,” she said.

“It would be good for our health and the environment if we drank less of them. In many areas, London has already been leading the charge in the battle to eat well. But we also need national action to ensure firms contribute to the overall health bill and encourage consumers to swap to healthier products. That is why we need a tax on sugary drinks,” she added.

In July, The Grocer revealed how Boycott accused the government of failing to tackle obesity caused by excessive intake of sugar and processed food, contrasting at the time the £1bn a year the industry spends on marketing to the “paltry” £14m spent on the Change4Life anti-obesity campaign.

She said the project planned to change “how and what” supermarkets and food manufacturers sell including financial incentives to encourage small food businesses to sell healthier food, families being given vouchers for fruit & veg and changes to store layouts “to make buying healthier food cheaper and easier.”

The Children’s Food Campaign claimed the revenue generated from a sugar tax could be used to set up a Children’s Health Fund, paying for programmes to improve children’s health and protect the environment they grow up in.

It plans to publish figures for the impact of a sugary drinks duty on the rest of England in early 2015.

“A duty on sugary drinks of 20p per litre would be the most practical and effective way of tackling a significant source of unnecessary calories and sugar in children and young people’s diets,” said campaign co-ordinator Malcolm Clark.

“Mexico, France and Hungary have already introduced a sugary drinks duty, and their citizens are reaping the benefits. Our politicians can no longer hide behind the idea that it wouldn’t be popular, or is an untried policy.”

But British Soft Drinks Association director general Gavin Partington said: “This is a poorly thought out political proposal which will hit the poorest hardest while doing nothing to curb obesity, the causes of which are far more complex than this simplistic approach implies.

“In fact, evidence from France shows that while sales of soft drinks initially fell after a tax was introduced in 2012, they have increased since, with sales up 6% in the first four months of this year. Policy should be based on evidence, not a tendentious report based on a flawed model.”