The group spread out along the walks, everyone settling to their preferred pace, and chatting all the way. It was blissful: fervent streams, lush green fields of glossy cows, winding stonewalls and remote farmhouses. It was only at the end when Wendy took us through some stretches that I remembered this was part of the exercise regime. Although the attitude was laissez-faire, Wendy’s gentle and cheery persuasion was hard to rebuff. A bit of “you can do it” mixed with “you will do it” ensured most joined the hike every day, and persuaded me to keep going back to her afternoon circuits class. The one-hour class went quickly with Wendy and Nik’s fun diversions and one-minute sessions of exercise ranging from short sprints to press-ups and squats.

It was exhausting but exhilarating and seemed like the regime would have a lasting effect on most of the people there. One of the group, Emma from London, had lost six stone since going on her first in:spa week last year. She’d adapted her lifestyle and credited in:spa with the change.

Between fitness we had cooking demonstrations from the lackadaisical chef Al, who showed us how to cook without using sugar, salt, oils, dairy and wheat, the diet we’d been following all weekend, alongside a ban on caffeine and alcohol. It surprised us all how tasty food could be without these additives and for many I think the meals were the highlight.

Food became a focus for many of the group. The intense exercise coupled with shrinking portions and removal of fatty desserts meant rumbling tummies, and when Al showed us how to make a healthy cake on day one, then didn’t serve it that tea time, it became something of an obsession, with people on more than one occasion asking when we would have it. It came finally as a treat at the top of Fremington Edge, and everyone was silent as we wolfed it down.

The recipe for the cake and everything else we’d eaten over the weekend, plus recipes for salads, soups, dressings and various healthy dishes were emailed to us on our return, to help us continue the good work. For some this didn’t last beyond the train journey. Hedge fund manager Richard relented over a KitKat from the trolley, although I was impressed to see that everyone else on the train to London ate the chicken mango salad pack lunch that Al had given us to see us home, shunning alcohol and even coffee. The support doesn’t stop there – Kathryn explained on the last evening that all of us would become in:spa members, giving us access to the website and invitations to yoga, fitness and cookery events in London.

On saying our goodbyes, kisses and hugs, we’d made friends and vowed to stick to our new lifestyle. One week on I’ve managed a dry week that ended only because of a wedding, when I succumbed to champagne and wine. Without sugar, caffeine, dairy and wheat I feel more energetic, alert and toned and while I accept that this radical detox will not last in the long term, I hope to have made some positive changes. It was with this in mind that sitting on the scratchy carpet of my local cricket club, surrounded by geriatrics valiantly attempting yoga, that I closed my eyes and tried to conjure birdsong over the groans and cracking knees, and smell freshly cut grass instead of smelly feet.

Need to know

In:spa (tel. 0845 458 0723) has two more retreats planned for 2007, on August 2-5 and September 20-23, and there are six retreats planned for 2008. Three days cost from £595, with the price rising to £895 for a single supplement and £695 and £995 for an en suite bathroom. The cost includes all accommodation, food and activities, but not transport to the venue or insurance. The retreat starts on a Thursday evening for dinner and finishes on Sunday afternoon.

Times recommends

• 10 of Rough Guides' best images
• How to do Florence for free
• The UK and Ireland's 25 best Christmas events