A Royal Marine Ultimate Boot Camp experience in Devon is a explanation

Ladies, on the count of three, I want you to fully immerse yourself in the water: One . . . two . . ." It"s 8.30am on a cold, wet October morning. I"m neck-deep in water, my stomach is rumbling and I"m dreaming of hot buttered toast. Breakfast, not full body immersion, is more what I had in mind.

"Three!" My group of 14 women, aged between 28 and 48, collectively obey and 30 seconds later emerge bedraggled, dishevelled, smelly and - remarkably - smiley.

Welcome to the Ultimate Boot Camp, or UBC, the only UK Boot Camp exclusively using Royal Marine personal training instructors (PTIs).

Mud larks: Cathy wades through a filthy river during her Royal Marine endurance test at bootcamp

With our first task complete, we carry on across, under and through various parts of Woodbury Common in East Devon, where Royal Marine recruits from the commando training base at nearby Lympstone undergo the rigours of basic training.

We run down steep gorges, up and along narrow trails with overhanging brambles, into and out of muddy streams - including one where we lie face-down and try to swim on our bellies - march in lines like soldiers, crawl on hands and knees through claustrophobic tunnels and race each other up steep, chalky inclines.

Through it all, we"re encouraged, directed and motivated by Head PTI Jon Stratford, 33, who leads the course, and Andy Duncan, 38, who assists.

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Two hours later, as we finish the Endurance Challenge - cold, filthy, drenched to the skin but elated - no one can quite believe it.

"It was the most satisfying, exhilarating, rewarding day of my life," says Sue Lawrence, 42, an antiques dealer from Bath, who had come on camp looking for a physical challenge. "When Jon said duck under the water, it was like life began again. I did it. Not my husband, not my parents. It was me," she says.

That"s the thing about Boot Camp: 80 per cent of it is about mental attitude. It"s also a chance, often for the first time, for women to totally concentrate on themselves and not their husbands, children or jobs.

For some, the switch from a lifestyle of on-demand caffeine and sugar - which are banned during the week - takes some adjustment, while others struggle to relinquish control.

Beauty camp: Although the exercise was hard, the Devon backdrop was awe-inspiring

Every activity, from six in the morning to nine at night, is planned with predictable military precision but information is kept to a minimum, with the group only told where to meet and what to wear.

Being late means an exercise punishment, like press-ups, for all.

The turnaround between the end of one activity and the start of another, including in some cases showering and eating, is rarely more than 45 minutes and can be just 15.

With little time to chill and daily physical activity that includes running, boxing, beach games, core stability exercises, circuit training, night walks and adventures, the anticipation builds over what will be served at each meal time. But calorific intake is limited to between 1,100 and 1,400 a day, partly to speed up weight loss for those who need it and to show that most of us eat too much anyway.

A typical day might include homemade-granola for breakfast, a mid-morning snack of sugar-free banana-and-date cookies, minestrone soup for lunch, an afternoon snack of roasted nuts and seeds, lamb casserole and vegetable for supper with a final evening snack of berries. Seconds, sadly, are out of the question.

Food isn"t the only comfort. Accommodation is in beautiful self-catering cottages at Higher Wiscombe. Once Hank Marvin"s estate, it"s now home to Alistair and Lorna Handyside, their three children, two dogs and all manner of fabulous wildlife, including badgers, bats, deer and more than 60 species of birds. It"s a memorable backdrop to 6am runs or afternoon circuits.

We"ve done it!: Relief and joy among the recruits after the course

But the week is not all about exertion. Physical activity is interrupted by lectures to help explain the physical and mental approaches to a healthy lifestyle, and a life coach arrives midweek for talks and one-to-one sessions.

For some it"s a highlight, for others it"s overwhelming. There are tears and, in some cases, the kind of tantrum any self-respecting six-year-old would be proud of. A combination of physical exertion, hunger, fear and exhaustion inevitably takes its toll.

But as the week draws to a close, frustration is replaced by joy as the benefits of six-and-a-half days of hard work and healthy eating reap obvious rewards.

"I"ve lost eight pounds and 91/ 4in from different parts of my body," says Sue.

Patti, a 38-year-old mother of two from London, amazes all. Overcome by events at the beginning of the week, by the end she"s nimbly climbing a 50ft wall and abseiling 90ft down the other side. Terrified and shaking, she does it anyway and then beams from ear to ear while phoning home to tell her sons what she"s accomplished.

And that"s just it. Boot Camp is as much about being faced with the seemingly undoable and finding the inner strength to do it anyway as it is about fitness.

"I"ve never experienced anything like this," says Sarah, 29, another mother of two, from Chelmsford in Essex. "And I don"t want it to end," she adds.

Judging by the tears in the car park as everyone gathered to say farewell on the final morning, neither did anyone else.

Travel Facts

UBC courses run from Friday to Friday in twolocations in Devon and Herefordshire. There are all-women and all-mencamps. Prices start from 1,275 for a shared room or 1,650 for single occupancy and include all meals, alltraining from Royal Marine PTIs, use of equipment and access to themembers" area. All travel is extra. For 2010 dates and more details,visit www.ultimatebootcamp.co.uk.

Where else to take it to the limit

Based in Dumfries and Galloway and in Andalucia, Spain, The Camp - which is run exclusively for women - promises participants will drop a dress size in a week.

Courses are run by ex-Special Forces military fitness instructors. Seven-day stays cost from 1,450 per person. For more details, see www.thecamp.co.uk.

The Alladale Fitness Retreat, an hour north of Inverness, offers six-night retreats including hiking, mountain biking,circuit training and boxing. Accommodation is in the luxurious Alladale Lodge with en suite rooms, sauna, games and living room. Prices start at 1,295 per person. For more details, visit www.alladale.com.

Not sure if you fancy an entire week of Boot Camp? Prestige Boot Camp runs Fitness Days in Bristol, where participants sample typical bootcamp activities such as circuit training, boxing, body pump, core training, team games, log runs, scramble net and obstacle courses. Week-long residential boot camps are also available for women, men or in mixed groups.

Fitness days cost 60 per day. Details at www.prestigebootcamp.com.