I am standing in the returns queue in Marks & Spencer. There is a certain amount of tight-lipped frustration in the air. I, on the other hand, am in an excellent mood. For once, I am happy to wait.

I get to the front of the line. I am returning items bought online, I explain. The assistant nods. I wait for her to ask me why. Instead, she begins scanning the labels. “There’s nothing wrong with them,” I volunteer. “They’re all fine,” I add. And then I can’t help myself: “It’s just that they’re too big.”

This has never happened to me before. I do a lot of online clothes shopping, see. When you’re a size 16, buying clothes over the internet is the least painful of options. I can try everything on in the privacy of my own bedroom, and if things don’t quite do up… well, that’s between me and the dog.

The clothes in question weren’t terribly exciting: a pair of work trousers, a top, a long cardigan. But they were definitely too big for me. Puzzled, I checked the labels. But no, it wasn’t M&S’s fault: it was me who was the wrong size. Tentatively, I reached for my bottom drawer. Here is where I keep my few remaining pairs of pre-pregnancy trousers.

I chose my favourite, from Whistles: a size 14. They did up, with ease. I sat down on the edge of the bed. A wave of pure joy washed over me.

Granted, a size 14 is not exactly sylph-like. But for me it’s a triumph. To have got there without any noticeable deprivation or insane exercise programme is even more thrilling. It has been a slow, gradual transformation, and I have just one person to thank: Susan Hepburn.

Hepburn is a hypnotist who specialises in neurolinguistic programming, focusing on weight problems. Back in April, we began with a detailed conversation about my life-long struggle to control my weight. Hepburn is both a perceptive and practical therapist. She asked me my ideal dress size. A 12, I replied. She laughed. Was I sure? Not a 10? Most of her clients wanted to be a 10. I stuck to my guns: a 12. Besides, I thought: it’ll never happen.

On my second visit she recorded our session straight onto my iPod, which I then listened to at home. We had our third session in June, and since then nothing. Except, of course, for the shrinkage.

If I think really hard about it, I can see how she has changed the way I eat. At work, when I go to buy coffee and my eyes greedily scan the array of treats behind the glass counter, I can hear Hepburn’s soft Barnsley burr, instructing me to “make healthy choices”. She seems to have done what years of diets and exercise regimes have never managed: to normalise my relationship with food. It is neither a source of comfort, nor an obsession; it is simply fuel. If I am hungry, I eat; if I am not, I do not. I have only one regret: I should have asked her to make me a size 10.

Susan Hepburn: 020-7487 5200

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