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Plans to tackle childhood obesity in England to be unveiled on Thursday will include aiming to cut sugar content in food and drink by 20% over four years, the BBC understands.

But measures, such as curbs on junk-food TV adverts, favoured by public health experts, are not expected to be in the strategy.

Sources say there will be more details about a tax on sugary drinks.

The document's publication has been expected for months.

'Radical policy'

Charities had called for wide-ranging measures, including:

restrictions on television advertisements

changes to rules on cut price promotions of junk food

a greater focus on exercise

The BBC understands the final plans will include measures to promote sport at school.

BBC health editor Hugh Pym said plans to cut sugar content by 20% over four years could be "seen as quite a radical policy".

But he added: "It is what is not there which will raise some eyebrows."

He said: "Campaigners will also say, 'Why on earth is this coming out in the parliamentary recess?'

"'The chancellor is away, the health secretary is away, the prime minister is away, does this suggest some lack of commitment to the whole plan?"

The strategy was proposed to tackle rising weights in children in England.

Meanwhile, plans for a tax on sugary drinks across the UK were announced five months ago, and sources say there will be more details on England's plans for this levy on Thursday.

The devolved administrations in Scotland, Wales and Northern Ireland will decide separately on how to spend their share.