The winter’s thawing, but the flab won’t melt. In the nude it looks as if you’re wearing flesh-coloured jodhpurs. The gym treadmill bores you senseless. (What are you? A hamster?) As does calorie counting. You like walking and cycling, but London roads are blocked with standard parental-issue behemoths burping exhaust fumes in your face.

An adventure holiday seems an innovative solution. A vacation that involves exercise means only one thing: guilt-free gluttony.

Dartmoor National Park is mysterious, beautiful and casually strewn with 3,000-year-old Bronze Age villages. On the first morning of my three-day exercise-athon, fluffy clouds were scudding across an azure sky, a perfect day for cycling. To me, bicycle riding conjures up images of berets, onion strings, striped shirts and Edith Piaf. After about an hour-and-a-half of mainly downhill pedalling through the spectacular, craggy scenery, I asked, casually, if we were nearly back at Princetown.

“Oh no,” my guide from Devon Cycle Hire laughed. “We’re not even halfway yet.” The look on my face must have registered more surprise than the congregation at Michael Jackson’s wedding. “We’re doing the 20-mile loop ride, via the lake.” He pointed to a distant patch of blue a few counties away.

I flumped backwards in a fugue of shock, my eyes bare and round as light bulbs and made a noise like a tyre going flat. “Well, let’s just turn and go back,” I pleaded.

“Oh no,” my guide cheerily explained. “It’s much harder to go back as it’s all uphill.”

Three hours and 14 miles later, I felt I’d been sodomised by a herd of elephants. Numb labia, I discovered, is not a town in Africa. My legs were also black and blue. Whacking your shin on a bike pedal hurts a lot, but it’s no more painful than, say, childbirth. To make matters worse, my trouser leg got caught in the bike chain; now that’s what I call a “vicious cycle”.

Dartmoor may be beautiful, but it’s also treacherous.

Dark fell suddenly, like a curtain. With the mist looming in the gloaming and the wind moaning like the Hound of the Baskervilles, I started squeaking like a lost kitten. But my sense of achievement at finally making it back to civilisation was immense. As was the meal I ate at the elegant Browns Hotel restaurant.

I’d been worried that an adventure holiday would mean sleeping in the kind of rustic hovels that resembled the home of the Clampett family before they left for Tennessee. But Browns, in the historic town of Tavistock, is a charming boutique hotel. This restored 17th-century coaching inn bottles its own water, drawn from a Roman well, viewable through a glass panel in the floor of the Orangery brasserie. But, soggy with dew, water was the last thing I needed now. With the restraint of an Exocet missile I was out of my clothes, and into a bottle of red. Having exercised so strenuously meant that I could devour the delicious à la carte menu with no qualms. The excellent fish, meat and vegetarian dishes are all sourced from local organic produce. All that frantic pedalling meant I could even indulge in two delicious puddings.

I awoke on the second day to a morning so misty that I couldn’t even see the moor, a bit of a worry as I was scheduled to go “cliff running”. I can’t believe that extreme-sports enthusiasts, otherwise known as “organ donors”, haven’t taken up “cliff running in fog” as the ultimate risk-taking thrill.

What else was available? I wondered. Richard, my ebullient guide from Breathing Space adventure holidays, suggested horse riding. “What?” I replied. “As an alternative to suicide?” It seems to me that horses are clearly superior to human beings; they aren’t stupid enough to bet on us, are they? Of the many activities on offer — surfing, climbing, mountain biking, coast-steering and hot-air ballooning — trekking seemed the least hazardous... surely?

Planning is a vital part of any trip. Just ask Scott of the Antarctic. What I hadn’t understood about Dartmoor is how quickly the weather can change. My little designer parka was not up to the onslaught of wind and rain. When it was revealed that I was scheduled for a six-hour hike, my reality cheque bounced. I suggested legging it cross-country straight to the pub. But my travelling companions, all hearty types, gave me a look that could have parted the Dead Sea.

That night it was more guilt-free noshing at the Horn of Plenty, a luxurious country hotel, set in five acres of wild orchards over the Tamar Valley. The award-winning restaurant uses organic vegetables and fruit grown in the master chef Peter Gorton’s own garden. Roast loin of Devonshire lamb with wild mushroom salsa, basil-flavoured mash, in red wine and garlic froth, melted away all the aches and pains brought on by all that exercise.

I left London fat and came back fit. The fastest technique for looking younger and slimmer is to be seen out only with much uglier women. But if you want a more lasting effect, get thee on an adventure holiday to Devon.

Need to know

www.discoverdevon.com (holiday line 0870 6085531) for information on exploring a greener Devon, award-winning accommodation, and the finest local food and drink.

Kathy Lette’s latest novel is How to Kill Your Husband, and Other Handy Household Hints (Simon & Schuster, £7.50)

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