Ministers have confirmed plans to push ahead with a sugar tax on soft drinks despite opposition from industry.

A Treasury document confirms the tax will be introduced from April 2018, with legislation put into the Finance Bill next year to pave the way for it.

In March, the Government announced it would introduce a sugar tax on the producers and importers of soft drinks with added sugar.

Drinks with 5g of sugar per 100ml will face a lower rate of tax ,while those with more than 8g per 100ml will face a higher rate. These rates have yet to be set.

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.

Pure fruit juices will be exempt as they do not carry added sugar, while drinks with a high milk content will also be exempt because of their calcium content.

Alcoholic drinks with an alcohol by volume of up to 1.2% (ABV) are included in the levy although some of these drinks will be exempt.

The document said: "A levy on soft drinks will contribute to the Government's plans to reduce childhood obesity by removing added sugar from soft drinks.

"The levy encourages producers of added sugar soft drinks to reformulate their products to reduce the sugar content, reduce portion sizes for added sugar drinks, and importers to import reformulated drinks with low added sugar to encourage consumers of soft drinks to move to healthier choices.

"If they do this, producers and importers of added sugar soft drinks can pay less or even escape the charge altogether."

The tax is expected to net £520 million in 2018/19, with a further £500 million in 2019/20 and £455 million in 2020/21.

The document added: "The implementation of a soft drinks industry levy is expected to add around a quarter of a percentage point to Consumer Price Index growth in 2018 to 2019.

"Overall, the levy is expected to have a positive impact on the health of individuals in the UK."

Over the weekend, British Soft Drinks Association director-general Gavin Partington said: "Evidence worldwide does not suggest that taxes of this sort have any impact on levels of obesity.

"However, we will review the legislation when published and will continue to work with Treasury officials during the process of implementation."

The Taxpayers' Alliance labelled the sugar tax an "ill-thought-out reaction" to pressure from the public health lobby.

Chief executive John O'Connell said: "Lasting change will happen via a long-term cultural shift, not by burdening the poorest families with a higher cost of living."

But, responding to the announcement, Alison Cox, Cancer Research UK's director of prevention, said: "The sugar tax isn't law yet but it's already started to work. Companies are reducing the amount of sugar in their drinks and with the details of the tax published today we can expect many more to follow suit.

"The tax provides an incentive for companies to create healthier choices - making reduced sugar products an easier option for the public.

"With the number of obese children reaching record levels, the health of the nation is in the balance. But the knock-on effect of a sugar tax is huge. Our projections show that a 20% tax on sugary drinks could prevent 3.7 million cases of obesity over the next decade."

Faculty of Public Health vice president Professor Simon Capewell said: "We urge ministers to set the levy at a rate where it will affect demand for products that have damaged our children's health and teeth.

"The nation and the NHS are facing an obesity epidemic that will condemn many children and young people to lives scarred by conditions such as type 2 diabetes and heart disease.

"Taxes on tobacco have been an important weapon in lowering smoking rates and we must be prepared to deploy similar tactics in the ongoing battle against what promises to be one of the 21st century's greatest health challenges.

"However, this is only the first step. We need a comprehensive obesity strategy with a range of effective, targeted measures."

In August, the Treasury published the results of its consultation into the tax.

It said some respondents claimed the rule exempting fruit juice "did not go far enough" and that fruits such as blackcurrant need added sugar to be palatable "due to the astringent taste".

Some argued blackcurrants have a high vitamin content and that drinks using the fruit should be exempt from the levy "due to their health benefits".