Estimates that half the UK population will be obese by 2050 "underestimate" the problem, a report has claimed.
The National Obesity Forum said Britain was in danger of surpassing the prediction contained in a 2007 report.
The lobbying group is calling for hard-hitting awareness campaigns, similar to the approach taken to smoking, to try to stem the problem.
Chairman Prof David Haslam said the crisis could get even worse than the "doomsday scenario" already set out.
The report stated: "It is entirely reasonable to conclude that the determinations of the 2007 Foresight Report, while shocking at the time, may now underestimate the scale of the problem."
The forum called for GPs to proactively discuss weight management with patients, and routinely measure children's height and weight and adults' waist size, it added.
Prof Haslam 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."
He added: "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."
Prof Kevin Fenton, director of health and wellbeing at Public Health England (PHE), said obesity was an international problem that required 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," he said.
"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."
A survey published in 2012 found that just over a quarter of all adults (26%) in England are obese. A further 41% of men and 33% of women are classed as overweight.
Tam Fry, also from the National Obesity Forum, told the BBC that foods needed to be "reformulated" as they were packed with sugar, fat and salt.
He said: "The problem with industry is that they're very happy to go on doing this unless they are actually whipped into shape and the only people that can do that is government.
"That is not to take away from the individual responsibility, but the individuals can only buy the food that is there on the shelves."