More than a third of NHS trusts have failed to sign up to a scheme to cut sales of sugary drinks in hospitals, new figures show.
NHS England said 80 out of 232 trusts have not yet joined the voluntary programme, which aims to reduce the number of sugary soft drinks, milkshakes and hot drinks with added sugar syrups, to 10% or less of all beverages sold across its sites.
The body has warned of a ban on sugary drinks in hospital canteens, shops and vending machines if the target is not met.
Hospitals and retailers were given until the end of March to take action to reduce sales and told a ban could come into effect on July 1 if progress has not been made.
The new figures come ahead of the introduction of a tax on sugary soft drinks on Friday.
NHS England chief executive Simon Stevens said: "We now know that obesity causes 13 different types of cancer as well as heart attacks and strokes, so the NHS has needed to get its own house in order on the epidemic of flab.
"Once the Easter eggs are gone, the NHS will be getting on with ensuring our hospitals and their retailers are offering healthier food and drinks for patients, relatives and staff."
National suppliers including WH Smith, Marks & Spencer and Greggs have signed up to the NHS voluntary scheme to cut sales of sugary drinks, along with 152 of 232 trusts.
Last year, Mr Stevens also ordered hospitals to remove super-size chocolate bars and "grab bags" of snacks from sale in a bid to tackle obesity.
The changes have led cafe chain Costa to stop selling the largest size of some of its drinks in hospitals, while thousands of chocolate bars have been removed from shelves and several retailers have been encouraged to reduce the number of calories in sandwiches, NHS England said.
Professor John Wass, from the Obesity Health Alliance, said NHS England was "leading by example when it comes to tackling obesity".
"The reduction in sales of unhealthy food and drink in hospitals is an important step in the battle against obesity," he said.
"It also sends a strong message that the NHS is serious about cutting the amount of sugar in the nation's diet."