The UK government has announced plans to introduce a surprise £520m levy on sugary drinks to tackle the country's burgeoning obesity problem.

Delivering his spring budget today, chancellor George Osborne said the average UK five-year-old consumes their own body weight in sugar every year and measures must be taken to prevent this.

"Doing the right thing for the next generation is what this government and this Budget is about," Osborne told MPs.

"No matter how difficult and how controversial it is. You cannot have a long-term plan for the country unless you have a long-term plan for our children's health care."

A sugar levy will be introduced on soft drinks from 2018, giving drinks companies – whose shares were sent tumbling by the news – time to adjust. The chancellor said there will be two bands for the levy – which drinks companies can choose whether to pass on to consumers – and added that pure fruit juices will be excluded.

Expected to raise £520m, the money will be used to double the amount spent on school sports. In addition, schools will be able to apply for money to extend the school day with more sports activities.

The announcement comes as a surprise as it was initially thought that the government preferred a product reformulation approach to direct tax on sugar products. The government's much-delayed Childhood Obesity Strategy had been expected to eschew a sugar levy until today's announcement.

The measure marks a major win for anti-sugar campaigners including celebrity chef Jamie Oliver, who have placed increasing pressure on the government to take decisive action.

We did it guys !!we did it !!! A sugar levy on sugary sweetened drinks ...... A profound move that will ripple around the world ....business can not come between our Kids health !! Our kids health comes first ..... Bold, brave , logical and supported by all the right people....now bring on the whole strategy soon to come ... Amazing news #jamieoliver

A photo posted by Jamie Oliver (@jamieoliver) on Mar 16, 2016 at 6:32am PDT