Jenni Murray: A big girl with the XL factor - eat your skinny little heart out, Britney

So, eat your skinny little hearts out Britney, Christina and Kylie. Michelle McManus - built like the eponymous 1970s wrestler Mick - is a Big Girl and a pop idol. Who would have thought we would see such a phenomenon when the female norm in popular music has become a galloping hairgrip, prancing around on Top of the Pops and showing off far too much of what little she has?

There's no doubting the talents of this statuesque young woman. Let's not call her fat - it's such a gross way to describe another person and only someone who knows the agonies of battling their weight (me) could draw empathetic attention to the poisonous power of the word. She has great charm and a terrific voice, and oozes what one judge, Simon Cowell, described to me as "the X-factor". She makes your skin tingle when she sings.

She has wit too, but then that's the Big Girl's shield. When Michelle makes light of seeing her face on the back of the promotional bus which carried her around the UK over the past week, she is joking in that-self deprecating way which says,"Let me get the insult in before you do, then it looks as if I can laugh off the slight that I look like the back of a bus and am consequently a greedy, over-indulgent, idle slob".

So - before we get carried away at the thought that Michelle's elevation signifies an easing of the pressure on the young to emulate the absurdly toned, slender, sexy images of the current crop of pop stars - let's consider how tough Michelle will have to be if she makes it and manages to stay at the top.

She has, we read, already lost three stone since the start of Pop Idol, which suggests she is not entirely content with the way she looks. She has had to endure the tabloids calling her "tubby", "a fat lass" or "grossly overweight". One of the judges, Pete Waterman, has been dismissive of her from the start and railed against her selection for the finals, claiming she had survived on public sympathy not talent.

Simon Cowell, who has supported her all along, let slip in an interview with me that Pop Idol had set out on this series to look for something "a bit different". So, will Michelle find herself just as cynically manipulated into her Big Girl's image as skinnier stars have been into the sex-bomb role? It seems a woman of any shape or size has to be tough and, preferably, bloody-minded to resist the moulding tentacles of the music industry. The precedents in the business are not encouraging, especially for the "plus-size diva".

Alison Moyet still has something of a career. Two other Big Girls succumbed to the pressures early on. Trawling through the internet for biographical notes on Janis Joplin, I found an alarming number of references to her being "dog ugly" and "just plain fat". She, of course, developed a fondness for every stimulant on the planet, with a particular partiality to Southern Comfort. She died in 1970 at the age of only 27.

Mama Cass, like Michelle, had a fantastic sound but I remember, to my shame, that in the cruel heartlessness of youth I went along with the consensus that the Mamas and the Papas women were "the pretty one" and "the fat one". Mama Cass died in 1974, aged only 32. She had had a heart attack.

There will be no worried parents looking at Michelle in her carefully chosen cover-all outfits, anxious that their eight- and nine-year-olds will want to emulate her. No one will be asking her - as I recently did Britney Spears - about the irresponsibility of presenting a highly sexualised image to young fans. By the way, Britney, whom I doubt was at the front of the queue when the intellect was handed out, was terrifyingly dismissive and told me that parents should trust their children. Not so easy, Britney, dear, when they are pre-teen and dressed as sex-offender fodder. Judging by the common sense Michelle has shown so far, she is neither so stupid nor naive.

But, I'm afraid, neither is she the ideal alternative role model. Only last week, official statistics confirmed that children are fatter than ever before. Almost a third of youngsters aged between two and 15 are overweight, one in six of whom is classed as clinically obese. It adds up to a 50 per cent rise in the proportion of children with weight problems in less than a decade - caused, as we all know, by too much junk food and too little exercise. Sport Idol, anyone?