Britons spend billions of pounds a year on trying to slim but studies have shown that more than four out of five people who start a diet end up piling the weight back on – and some put on even more besides.

Ann Widdecombe is no stranger to trying to lose weight, but she is adamant the best way to shift the pounds and stay slim is to eat less and move more.

She tells the programme: “At London fashion week…the girls with bodies to diet for are everywhere. But let’s face it – 99 per cent of us have no chance of looking like this.

“So why do we spend billions of pounds a year trying to achieve it? Why do we put our health, happiness and sense of well being at risk?

“And why – when it all fails – do we try it all over again?

“Never before has the nation been so obsessed by slimming. It’s the one subject guaranteed to keep tills ringing, and the sales of glossy magazines soaring.

“The message is loud and clear – to fit in, we must be thin.”

In Ann Widdecombe Versus the Diet Industry Widdy meets women who have tried a variety of ways to stay slim, only to end up fatter than when they began.

She also hosts a dinner party for four people on an assortment of diets and with the help of Dr Mark Hamilton, she looks at potential health risks of these diets.

Ann tells the programme: “Well, I’m certainly not a regular reader of the celebrity magazines.

“What I cannot believe is the nature of some of the diets being promoted. The baby food diet? The maple syrup diet? Can anyone really take that seriously?

“But an even bigger shock is the sheer level of the obsession with which these magazines promote diet after diet.

“From our survey of 90 magazines, there were an astonishing 74 headlines about diet and body image on the front covers alone.”

She then tackles a magazine style editor to ask why glossy magazines constantly promote diets and weight loss and regularly feature celebrities with very thin body shapes. When Ann asks her how many women who are a size 16 feature in her pages, she suggests taking a look inside to see. She keeps flicking the pages, but turns up a big, fat zero.

Believing many of the obsessions with body size adopted in this country originate from Hollywood, Ann jets out to California to meet Wendy Brown, extreme make-over consultant to the rich and famous, who explains to her what she would need to do to herself if she wanted to make it big in Hollywood. And she visits a plastic surgeon who presents her with the computer generated image showing her how the movieworld Widdy would look.

Closer to home, Widdy interviews Anne Diamond and challenges her about her lucrative career based on her continuing battle with the bulge. Ann describes how Anne Diamond brought out a fitness video after losing weight, put the weight back on, then brought out another fitness video after losing the weight again.

Anne tells Widdy she is now a size 16 which prompts Widdy to ask if she is pedalling a yo-yo diet lifestyle.

Anne Diamond replies: “No. I think I’ve been typical of a lot of women of my age, women and men and that’s all I’ve been is typical. What I think I am doing is just being me, being one of us and trying to do my best and each time I am learning. But what I am saying is ok, my weight is part of my public profile sadly – I will at least be open about it and say where I went wrong so that hopefully others can learn as well and I am learning too.”

Widdy questions Anne’s website which offers moral support for other people struggling with their weight, but also features a range of weight management products.

However, Anne insists she does not promote these products saying: “It’s an acknowledgement that there is a commercial world out there and we have to promote just general talking about it. It’s an open exchange of views and lots of people can write in and they can get trial products… just as long as they review it.”

In Ann Widdecombe Versus the Diet Industry, Widdy also works with psychologist Dr Linda Papadopoulos – who believes a daily diet of magazine images is harming our young people – to boost the self-esteem of a group of schoolgirls who suffer from negative body images.

Ann and Linda visit the girls at their school in Surrey where Linda asks them to fill in surveys about how they view their bodies and looks. An average score would be around 30, but all of the nine girls score at least 50, which means they are all expressing negative thoughts about themselves.

The girls are then asked to flick through magazines for twenty minutes before filling the surveys in again. Ann is shocked to discover their self-esteem plummets even lower and some of the scores are coming out as high as 85.

One girl tells the programme: “For me personally it’s pretty important to be skinny and slim, basically more people would like me, I can wear nice clothes and you get more compliments I think.”

Linda tells Ann that she believes it is vital to change the teenage thought process and would like to see a body image education program rolled out in schools across the country.

She says: “What we’re trying to do is go into schools and adapt a part of the curriculum that addresses young people’s self esteem, I always found it interesting that we teach them the names of obscure rivers here and there but we don’t teach them how to look at the issues day to day about liking ourselves or not, about rejecting or accepting ourselves.”

In the programme she decides to work with the group of girls in Surrey to see if she can turn their negative thoughts around. She encourages the girls to focus on their attractive qualities and write down things that they like about themselves. She then asks the girls to complete the surveys again – will she be able to reverse their negative thoughts and undo the damage done by the magazine images?

And Ann meets two girls whose weight fell below six stone when they began dieting and didn’t know when to stop. They tell Ann that they would buy magazines for tips on how to lose weight like celebrities.

In France the government are so concerned about anorexia that new legislation is expected to be approved which will make it a criminal offence to “encourage another person to seek excessive thinness” and that law would apply to magazines.

Ann says: “In Britain, I’d even be happy with a voluntary code of conduct.

“Here eating disorders continue to increase and anorexia is believed to have one of the highest mortality rates of any mental illness…. killing 20 per cent of long term sufferers.”

Thursday, 25 September 2008, 9:00PM – 10:00PM, ITV1