In a letter sent to the trade alongside the pledge, Dr Susan Jebb, co-chair of the Responsibility Deal Food Network, gave businesses two weeks to respond with early commitments. She said the pledge "provides a mechanism for business to deliver its crucial contribution, alongside government and others, in helping the population meet the calorie reduction challenge".
The pledge is part of the government's wider Public Health Responsibility Deal (PHRD). It suggests ways to reduce calories in products, including reducing fat and sugar content; cutting portion sizes; developing lower calorie options and using satiety ingredients.
Malcolm Clark, coordinator of Sustain's children's food campaign, called the pledge "a cop out", which made too many concessions to the food industry. "I'm very under whelmed by it. It's a real step back from what was happening on salt targets." It provided no firm targets or time scales with which to hold industry to account, he added.
Some processors also expressed scepticism about how effective the pledge would prove. "It's a little woolly," said one. "The brief was manufacturers should largely design their own standards." He added: "We can reduce portion sizes, but what's to stop consumers buying two portions?"
Many firms claimed it was too early to pledge their support, although Food Manufacture understands some high profile brands have already committed to it. A spokesman for Kraft Foods said the company was committed to the PHRD. "But we have only just received this final draft, so will review it thoroughly before making any further comment."
Mars made an unrelated global commitment last month to stop selling chocolate bars containing more than 250 calories and said it was considering the pledge.
Own-label producer Greencore, said it supported the PHRD, but had to canvass retailers' views.
Terry Jones, Food and Drink Federation communications director, said: "Building on their existing work on public health, our members will be looking closely at the pledge to establish how they might credibly respond to the government's call to action on obesity launched last year."
That document challenged the population to cut total daily calorie consumption by 5bn calories and the DoH aims to reduce the growth in overweight people by 2020.
Soft drinks firms would sign the pledge only if they believed "their actions and achievements can be properly explained under the DoH format", said a British Soft Drinks Association spokesman.