After years of trying and failing with various new workout plans, Sarah Vine has finally found 'the one' - and what's more, she's sticking with it

Regular readers will know that, when it comes to diet and exercise, I have the attention span of a gnat and the willpower of a toddler. On numerous occasions I have bored you with gushing accounts of how I have finally managed to find a regime that suits my chaotic life , age and temperament - only to find myself straight back at square one within a matter of weeks .

But the reason I've been so quiet lately is that this time it's all true. I have found The One. My fitness nirvana. The one thing that not only works - but that, far more importantly, I can actually stick to.

Truth is, exercise is like men. There's no accounting for taste. Susannah , for example, likes to run triathlons . I would rather boil my head. I have another friend who loves riding. Personally, I can't stand horses. Yoga? Alright if you don't mind other people's feet, which on the whole I very much do.

As with men, it's also important to learn from your mistakes. I may fancy myself as the sort of woman who can do 100 lengths in the fast lane of my local pool, but the only physical change I experienced from swimming was the appearance of a verruca on my foot. And sure, I would like to think of myself as a runner, but the reality is the bra has not yet been invented that can make jogging comfortable for me.

Getting it right means knowing yourself, your strengths and your limitations. It means finding something that does not require a hugely impractical lifestyle change, or relocation to California. It means finding something you can stick with through the ups and downs and daily vicissitudes of ordinary life. In short, something that can become as much a part of your daily routine as brushing your teeth or tying your shoelaces.

This has only ever happened to me once in my life, when I met David Higgins, the Pilates trainer. For years I relied on David to keep me in shape. But then my health deteriorated for a couple of years, and even that became impossible. By the time I resurfaced, he had left Ten Pilates, and it just didn't seem the same without him.

I found myself in a kind of fitness wilderness. Nothing I tried seemed to work, or it made me too tired or caused injuries. So when I first met Zana Morris  of the Library Gym , I was pretty much on my last legs. I felt old, knackered and fat. I was tired, grumpy, restless and motiveless.

Not for much longer. After just 12 days on her kick-starter programme, I was transformed. Energised, slimmer, enthused and annoyingly evangelical about her programme. I wrote about it for Get The Gloss .  And then, I rather assumed, I would move on and go back to my old ways - before doing it all again with someone else six months later.

But that hasn't happened. Yes, it's expensive, at over £500 a month, but I am still there, wafting back through her door every morning like a bad smell. I go four days a week, come rain or shine, sick children or work crisis. Unless I am not physically in the country, I cannot wait for my morning fix. It's like coffee: I'm not quite myself until I've done my workout.

There are several reasons for this. Firstly, it's fast. Very fast. 15 minutes, all told. I'm in and out in the time it takes some people to choose what to have for lunch.

Secondly, no two sessions are the same. The team of trainers on constant call keep a very, and I do mean very (no cheating) close eye on what I'm doing. They're forever changing weights, adding or taking away bits of the routine, tweaking here and there.

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Thirdly, results: I'm getting them. I've lost two inches on my upper arms. About four on my stomach; half an inch on my neck; even my feet have slimmed down. My clothes are getting bigger - but I'm not feeling the effort. I look healthy, and I can walk up the hill behind my friend's house in Somerset without getting out of breath. My body, which I had all but given up on, works again - and it really is one of the most exhilarating feelings in the world.

Fourthly, food. I'm still allowed to eat it, which is a great relief. And while the diet side of the package is definitely my weak spot, I enjoy the training so much I know it's not the end of the world if I accidentally give in to a glass of wine or a passing pavlova.

Friends are amazed. Not just at the difference it's made, but at my ability to stick to it. 'My god,' they exclaim when they see me, 'don't tell me you're still doing your thing!'

Several have even followed me, with similar positive results. One, who, laid low by IVF and illness, arrived there drawn and in pain is a new woman. Another, always slim but not as fit as she would have liked to be, now has small but perfectly formed biceps. Husbands have started joining in too.

There's another reason it works, too. It's not gimmicky or pretentious. It's just good, sound sports science, combined with expertise and a very large helping of charm. No one dresses up (apart from one Russian lady, but we forgive her) or shows off. People bring their dogs and children, who wait in the garden or loaf around until you're done (it's so quick, they never mind much). There is tea, coffee and - another great motivator - regular weighing and measures, just to make sure things are all going in the right direction.

I still don't have a perfect figure, and I probably never will. But Zana and her team have given me back my body, and for that I cannot thank them enough.

Zana's team work at The Library Gym in London. Membership is £550 a month.

Buy Zana Morris's book, The High Fat Diet on Amazon here

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