Sarah Vine's mission to lose weight might finally be paying off...

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First day back on the weight-loss wagon, and the universe decides to offer me a stay of execution. Personal trainer Steve , he of the contraptions and ball of fat, is indisposed. He has run the London Marathon, see. Somewhere around the 24th mile, one of his toenails fell off.

Most normal people would have collapsed in agony and spent the rest of the day wrapped in tin foil drinking hot chocolate laced with whisky and codeine. But Steve is not normal. Oh no. He is Steve. So he just carried on. Yes, readers, he ran the rest of the marathon without a toenail.

MORE GLOSS: The Get Running app

What can we learn from this incident? First, running is, as I have always believed, an unnatural activity if taken to extremes. By which I mean anything more than a fast stroll around the park. Secondly, Steve is clearly a bit nuts.

Two days later, he is back in action. Which means I'm doing squats. It's horrible. What little progress I had made before my holiday has vanished. My breath feels like razor blades in my lungs and my heart is pumping fit to burst. After three gruelling rounds of squats, press-ups, ball throwing and silly walks, Steve allows me a rest.

I sit down to catch my breath and a man strolls by smoking a spliff and chatting on the phone. Pretty edgy for half past ten in the morning, but I guess that's Wormwood Scrubs for you. As I watch him saunter off into the undergrowth, Steve says, "You have lost a bit of weight, you know." Yeah, right, I think. You must have inhaled rather too much of that bloke's joint.

MORE GLOSS: Sarah Vine on her mission to lose weight

Nevertheless, back home, I cautiously approach a pair of silk satin palazzo pants  that hitherto have made my legs look like shiny black puddings. I love these trousers: the fabric is cool and the cut is simple and chic. I bought them earlier in the year, and they're precisely the sort of thing I would be wafting around in if I weren't such a lard-arse.

As if by magic, they glide on easily. The fabric is looser than I remember, and the waistband doesn't cut into my stomach. I wouldn't say they look fabulous; but they don't look hideous either. With a longish top, I feel I could actually wear them.

Click here to read  part one ,  part two  and  part three  of Sarah's weight loss journey.