Following Ofcom's ten-week consultation into possible measures to cut food and drink advertising to children, the body has proposed a series of restrictions.
Junk food ads will be banned from air during programmes aimed at children, and in programmes of particular appeal to children up to nine years old.
Ofcom will also ban all food and drink advertising in programmes made for pre-school children, and limit such advertising when children are most likely to be watching.
But Which? claims this will not provide adequate protection to young children targeted by food company PR specialists.
"Food companies will still be free to bombard kids with junk food ads because the proposed ban won't apply when most kids are watching TV," Which? warned yesterday.
New research conducted by the watchdog shows that more children aged nine and under watch TV in the evening than during specific children's programming schedules.
It took a snapshot of ITV1 viewing figures over a two week period in February, and found that in the four to nine age group the most popular programmes were family-orientated, such as soap operas Emmerdale and Coronation Street.
Four times as many under-10s watched family show Dancing on Ice one Saturday evening than children's programme Spongebob Squarepants on a Saturday morning.
But under Ofcom's proposed measures, food companies will still be able to advertise unhealthy foods during these peak viewing times.
Which? chief policy advisor Sue Davies, said the proposals "are a total sham."
"They have set out three options, all of which fail to tackle advertising of unhealthy food during the programmes that most young children are watching, and none of which consider that older children deserve protection too."
Which? wanted a complete ban on junk food ads during the hours that children are watching television - not just during children's programming.
The organisation is now calling on the government to intervene and is urging parents to join its kids' food campaign and email Ofcom with their views.
Nearly one third of two to 15 year-olds in England are now classed as overweight or obese, sparking concerns of an epidemic which could lead to a variety of fatal illnesses in later life, including heart disease and diabetes.
Research has shown the eating patterns that cause obesity begin in childhood, with evidence growing that people's lifelong eating habits are largely in place before they are 10 years old.
Worldwide over 22 million children under five are severely overweight. Experts say junk food and low exercise levels, combined with the popularity of computer games and television, are behind the growing obesity rates.