So I’m lying face down in the mud in a freezing London park with a shocking hangover and two horrible teenage boys loitering nearby, nudging each other and laughing.

Rivers of sweat are pouring off me, every muscle aches and I don’t have enough breath left to tell the boys to Foxtrot Oscar.

The worst thing is, I’m only half way through today’s exercise programme – and given that I didn’t so much fall off the wagon last night as jump off it head first, smashing every bone in my body in the process – I’m determined to finish this workout or die in the attempt (which currently seems a very real possibility).

Walking at a brisk pace for three hours a week can reduce risk of heart disease by 65%

I’ve already put myself through 45 minutes of interval training, pure torture on a day from hell like this, sprinting as fast as I can over increasing distances, with short rest periods in between, during which a killer headache pounds around my skull, my lungs feel like they’re going to burst out of my chest and it’s all I can do to stop myself weeping in abject self-pity.

Now I need to perform 12 press-ups, 14 lateral raises, 16 tricep dips, 16 bicep curls, 14 shoulder presses and 12 bent over rows; and not just the once either, oh no – I have to do three sets of each.

Under normal circumstances after a massive night, I would of course be at home on the sofa, tucking into a full English and watching daytime television, but since I blithely signed up to the challenge of dropping a dress size in two weeks using the New You Boot Camp as my guide and inspiration, there’s no chance of that.

If you must…Sara’s advice is to work out at a boot camp, away from temptation

I wish I had considered the inherent difficulties of following this plan during the two most social weeks of the year, when I invariably find myself rolling from one bottle of wine to the next, via cocktails and canaps not to mention huge lunches, dinners and late night snacks to soak up the troughs of festive booze. As it is, despite my weekly spinning, body pump and circuits classes, I’m finding the experience crazy hard.

No matter how well-intentioned I am at the start of each day, huge Christmas-shaped spanners keep throwing my good plans into disarray and the very sight of this irritatingly cheery book, with its case studies, motivational tips and horrid recipes, makes me twitchy.

3,500: The number of calories you need to burn to lose 1lb of fat

I have to train five times a week and when I haven’t overindulged the night before the exercise elements are fine, if monotonous – I find running beyond boring. The thing that makes me really mad, makes me think I don’t want a new me if this is the way to get it, is the food fascism – or nutrition as it’s called in the book.

If you follow this plan, chirrup the authors, your energy levels and mood will remain even throughout the day and you won’t feel hungry. This is a total lie: I was STARVING.

When I get hungry I get angry – and I was pretty livid from day one on the regime. Quite frankly, a raspberry and peach smoothie does not a breakfast make; nor does a snack of two oatcakes and one tablespoon of hummus a couple of hours later in any way take the edge off, especially after a workout.

Healthy maybe – but not very filling

By lunchtime I’m ravenous and the soup and chicken leg only intensifies my rage. My feelings about the meagre dinners of Spanish-style chicken or vegetable stew are unprintable in a family newspaper and I have to go straight to bed afterwards to stop myself devouring everything in the kitchen.

I could probably lose a few pounds but I’m far too happy as I am to starve myself like this and it’s making me miserable. On the fourth day I crack and Hoover up a whole French stick with lashings of butter – and oh my goodness, it’s amazing to feel full.

I’ve got to be honest and admit I only managed to follow the plan to the letter for eight days out of the required fourteen. There was too much on and it’s just not in my DNA to go to a party and stand in the corner with a glass of sparkling mineral water, or go out for lunch and have a boring salad whilst everyone else is tucking into delicious steak and chips.

Unless you have willpower of steel – in which case you don’t need to read this book anyway – I would suggest that the only way to enjoy success on a bootcamp regime is to GO on a bootcamp, preferably one run by a strict sergeant major-type in the middle of nowhere with no pubs, corner shops or transport links to aid escape.

Despite my many failings, however, I am delighted to report that although I did not drop a dress size I didn’t gain one either, which is unheard of as far as I’m concerned at this time of year. Bottoms up!*