Cranberry juice should be exempt from a future sugar tax due to its "exceptional health qualities", MPs have suggested.

Campaigners want sugar-sweetened soft drinks to be targeted by the Government as part of its measures to tackle the country's obesity problem.

The Downing Street policy unit is working to finalise plans dealing with childhood obesity, with Prime Minister David Cameron having hinted he is prepared to drop his previous opposition to a general sugar tax.

But MPs warn the amount of cranberry juice people drink could fall if such a tax is applied to it.

The Northern Irish group - containing four Democratic Unionists and the Social Democratic and Labour Party's Alasdair McDonnell - note cranberries are low in natural sugar and high in acid, meaning the juice needs to be sweetened to ensure people can drink it.

The DUP's Gavin Robinson (Belfast East) has tabled an Early Day Motion (EDM) in Parliament entitled "Health benefits of cranberries and the sugar tax", in which he calls on the Commons to recognise the "unique health benefits" of cranberries and their role in preventing urinary tract infections (UTls) in women and children.

The motion states: "(The Commons) notes that at least half of all women will have a UTI during their lifetime and will subsequently be prescribed antibiotics to treat the infection.

"(It) further notes that antimicrobial resistance is a growing issue of concern that unless tackled will make the most minor procedures dangerous, and overprescribing of antibiotics must be halted.

"(It) takes note that if simple infections such as UTls can be prevented in the first place the need to prescribe antibiotics will be reduced.

"(It) further recognises that, in their natural state, cranberries are low in natural sugar and high in acid and therefore need to be sweetened for palatability.

"(It) is concerned that any measure to restrict the promotion of juices with added sugar could have a detrimental effect on beneficial consumption of cranberry juice; and calls on the Department of Health to exempt cranberry juice from any measures to restrict promotion on sweetened juices due to its exceptional health qualities."

An EDM is a formal motion submitted for debate in the House of Commons, although very few are actually debated.