Predictions that half the British population will be obese by 2050 "underestimate" the scale of the obesity crisis, a report suggests .
The UK is in danger of surpassing predictions of a 2007 report which estimated that 50% of the nation would be obese by 2050, the National Obesity Forum said.
The "doomsday scenario" set out in the report does not cover the true extent of the problem, it said.
The forum's latest report calls on health officials to introduce hard-hitting awareness campaigns - similar to those for smoking - to try to stem the problem.
The organisation also called on family doctors to proactively discuss weight management with patients. GPs should routinely measure children's height and weight and check adults' waist circumferences, it said.
The report states: "It is entirely reasonable to conclude that the determinations of the 2007 Foresight Report (i.e. that half the population might be obese by 2050 at an annual cost of nearly £50 billion), while shocking at the time, may now underestimate the scale of the problem."
Professor David Haslam, chairman of the National Obesity Forum, said: "We're now seven years on from the Foresight Report. Not only is the obesity situation in the UK not improving, but the doomsday scenario set out in that report might underestimate the true scale of the problem.
"There needs to be concerted action. There is a lot more we can be doing by way of earlier intervention and to encourage members of the public to take sensible steps to help themselves - but this goes hand in hand with government leadership and ensuring responsible food and drink manufacturing and retailing.
"Initiatives such as Change4Life are very well intentioned and directed but cannot be expected to solve one of the great public health problems of our time on their own.
"We need more proactive engagement by healthcare professionals on weight management, more support and better signposting to services for people who are already obese, and more importance placed on what we drink and how it affects our health.
"We've seen hard hitting campaigns against smoking and it's time to back up the work that's already being done with a similar approach for obesity."
Professor Kevin Fenton, Director of Health and Wellbeing at Public Health England, said: "Obesity is an international problem. It is a complex issue that requires action at national, local, family and individual level.
"Everyone has a role to play in improving the health and wellbeing of the public, and children in particular. PHE are committed to helping to tackle obesity through a range of approaches that support action on the local environment to make eating less and being more physically active easier."
Labour public health spokeswoman Luciana Berger said: "With a third of children leaving primary school in England either overweight or obese, this report is right to call for radical action to tackle obesity. Unfortunately David Cameron has caved in to vested interests and his Government's approach is not working.
"There are too many products on the shelves which are presented as healthier options but contain higher-than-expected levels of sugar, salt and fat.
"That's why Labour is consulting on whether there should be limits on the amount of sugar, salt and fat in food marketed at children. If ministers fail to act, we are in danger of storing up major long-term problems for both our country and our NHS."