Jowell said the food industry has to take action to counter obesity

Speaking on BBC Radio 4's Today programme, she said she doubted that banning junk food TV ads would help tackle the problem.

But she said the food industry could help find a solution to the "crisis of obesity" and was expected to do so.

Experts have recently warned that as much as 40% of the population will be obese in one generation.

'Widespread concern'

Ms Jowell argued that individuals were responsible for their own diet and physical activity.

"The reason we have this crisis of obesity is because too many of us are eating too much of the wrong kind of food... and we are not exercising enough," she said.

The headlines are that Peter Hain and I are at logger-heads, there are 'choccie wars' Tessa Jowell

"The question that follows from that is whose job is it to do something about it."

She said both the government and the food industry had to take action, and that the latter was "very much on probation".

"I think there is widespread public concern about some of the marketing tactics that are used by the food industry.

"They are on probation and just as they are part of the problem, they too can be part of the solution.

"I have thrown down a challenge to them and said you come forward to us with your proposals as to how you can work with government, with the schools, in order to tackle this - to guide children to healthier eating and more healthy activity."

Questioned on why she was not endorsing a ban on junk food ads on TV, she argued she was sceptical about the effectiveness of such a measure.

But she pointed out she had asked broadcasting regulator Ofcom to review advertising codes to check if they were strong enough to protect the public and children in particular.

She also said that the apparent row with Welsh Secretary Peter Hain over a promotion by Cadbury last year which offered schools sports equipment in return for chocolate wrappers was being blown up by the media.

'No row'

Having an open discussion about a disagreement rather than one behind close doors was "healthy politics", she argued.

Referring to Sport Minister Richard Caborn and herself, she said: "We decided it was worth supporting because it would bring lots of money into schools to buy sports equipment".

But she acknowledged that the argument on whether or not the government should have made that decision was a "fair issue for discussion".

More than 100 British consumer groups have called for a ban on TV ads for junk food after it emerged that one in four men and one in five women are classed as obese in the UK.