Health experts have warned that the Scottish Government's deposit return scheme risks damaging the country's fight against obesity by encouraging people to buy larger bottles of fizzy drinks.

The scheme will see consumers pay a 20p deposit on single use cans and bottles, ranging from a 50ml miniature to a three-litre bottle, with the money being refunded when the containers are returned.

However, leading academics claim the 20p flat rate risks Scots choosing to buy larger volumes of sugary drinks, rather than paying the deposit for smaller items such as 330ml cans.

In a letter to The Herald, five health policy professionals have called for changes to be made to the plans, which aim to increase recycling across Scotland.

READ MORE: Scottish deposit return scheme: Cans and bottles to carry 20p deposit to save waste

They want to see a graduated deposit put in place which increases with the size of the container.

The letter - signed by Shona Hilton, professor of Public Health Policy at Glasgow University, and Professor Alec Morton, founding fellow of the Centre for Health Policy - states: "In a bid to boost recycling earlier this year Holyrood unveiled proposals for a deposit return scheme for drinks containers.

"A flat rate 20 pence deposit has been proposed for the vast majority of containers regardless of size - from 330 ml servings of lemonade to 750 ml bottles of sparkling juice and two-litre containers of cola. 

"For smaller servings of less than half a litre a 20 pence deposit represents a huge percentage increase on the price charged to the consumer. For larger containers the increase is less significant. 

"A flat deposit fee thus risks incentivising consumers to purchase larger containers of sugary drinks. This in turn could severely hamper the Scottish Government’s efforts to meet its targets on childhood obesity. 

"If we are to make meaningful progress in the fight against obesity and diabetes, we need a deposit return scheme alive to the realities of public health in Scotland today. 

"This means a graduated deposit which goes up in proportion to the size of the container."

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Plans for the scheme were announced last month by Scottish Environment Secretary Roseanna Cunningham who said it would be up and running by the end of the current Parliament in 2021.

The first such scheme in the UK, it will cover lass and plastic bottles, as well as aluminium and steel drinks cans, sold from any shop in Scotland.

It aims to capture 90 per cent of drinks containers for recycling within three years.

A “return to retail” service will be implemented as part of the scheme, with all businesses which sell drinks required to accept returns.

Ms Cunningham said that smaller retailers will be given flexibility in how they enable returns through different sizes of reverse vending machines or manual over-the-counter take-back arrangements.

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A Scottish Government spokesman said: "Tackling obesity is a priority for the Scottish Government and last year we published a comprehensive plan which sets out a wide range of actions to support people to eat well and have a healthy weight.   

“This includes our ambition to halve childhood obesity by 2030, our investment of £42 million in weight management services and proposals to restrict in-store promotion and marketing of foods high in fat, sugar or salt with little or no nutritional benefit.

“We were the first part of the UK to commit to a deposit return scheme which is ambitious in scale and scope and gives the people of Scotland a clear and straightforward way to do their bit for the environment.”

The other signatories on the letter are Strathclyde University's Dr Simon Hunter, fellow of the Centre for Health Policy, and Dr Joan Costa-i-Font and Professor Alistair McGuire, both of the Department of Health Policy at the London School of Economics.