We were on the ferry, returning from a break in Ireland, queueing for food. When I saw my husband's fish and chips, I decided I fancied some, too. But instead of the generous portion Evan received, I got a handful of chips and a piece of fish half the size. I didn't put the plate on my tray because I assumed the man at the counter hadn't finished dishing up. But instead of supplementing my chips, he told me, in an "all mates together" kind of way, that I shouldn't expect any more, as, by the looks of things, I'd had quite enough already. As those waiting to be served looked on with interest, I stood rooted to the spot, red-faced and deeply humiliated.

Today, I'm 38, 5ft 8in and weigh around 11 stone. I run 15 miles a week, as well as ride, swim and cycle, and I watch what I eat. But seven and a half years ago, things were different. I weighed around 21 stone and was barely able to get up stairs. I felt ill most of the time and the effort of heaving my bulk around and trying to catch my breath made normal activities a test of endurance.

I had battled with my weight - and the ensuing eating disorders - since my teens. However, it was only after meeting Evan at 21 that obesity started strangling my life. I'd had a contraceptive injection that, while protecting me from unwanted pregnancy, had the side-effect of helping me gain seven stone in 18 months. I won't pretend I didn't overeat, but the effect was to turn me from a normal young woman into a non-person.

Assistants on beauty counters would tell me that, although the product was designed to be toning, on my surfeit of flesh it would be a waste of time. Prospective employers, delighted by my CV and enthusiastic on the phone, would in person eye the straining buttons on my size 24 dress and say they didn't think I fitted the company culture.

When I went to the doctor with chronic pain in my shoulder, rosacea, eczema and bouts of nausea and vomiting - clear symptoms of a diseased gall bladder - my GP simply Googled the nearest Weight Watchers class and gave me the time and date of the next meeting.

The sad thing was that I believed I deserved it all. I regarded being obese as a sign of personal failure.

However, the mockery and dismissals didn't help with my dieting. What they did was feed an ever-growing obsession with food. The less a member of society I felt, the more I stuffed into myself. I was no longer validated as Madeleine, so I used the process of foraging for food in bins, and eating it behind locked doors or in toilets, in order to exist.

It wasn't all bad, of course. I did eventually get a job and, in 1994, I got married, but overridingly the memories of these years are dark. After having my second child, my self-esteem had sunk so low that I felt unable to return to work.

The tone of the government's new Healthy Weight, Healthy Lives strategy smacks of explaining something very simple to a slightly backward child. What it ignores is that most obese people have already tried and failed any number of diets, and know only too well what the extra weight they are carrying means for their health and personal lives.

Obesity is not the result of a lack of information or self-control; it stems from not valuing sufficiently yourself and the food you eat. Turning overweight people into national whipping boys will only drive further into the biscuit barrel those who already have little self-confidence.

It was after dieting unsuccessfully for several months that I came across an article about the gastric bypass operation. Despite evidence that morbid obesity is almost untreatable without surgery, the NHS was not prepared to fund this life-saving operation, so I remortgaged our house and paid the £8,000 myself.

It's amazing what losing 10 stones can do. Within a year I went from comic curiosity to real person again. I started an exercise regime and, as my skin and muscle tone improved, so did my confidence. Surgery had revealed the undiagnosed problem with my gall bladder and I won compensation from my health insurer for the treatment I received. I took on a senior role at work and, in 2005, started my own PR agency.

What I've achieved in the past few years shows I've always had drive, determination and self-discipline. It's just that in a society that excludes on the basis of body fat, none of that was recognised.

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