MONDAY JANUARY 28

Odd call from Telegraph. Want writer to visit fat camp in Devon for week and - much polite hesitation before getting to point - thought of me.

What? Am I really fattest freelance in Britain? True, 15st 6lb is on heavy side as am 5 ft 8in tall, but surely am just naturally stocky? All right, maybe could lose pound or two. Nice to go home for Christmas without reminders from Mum that Grandad had first heart attack at my age (43).

Don't hold out much hope, though. Over years, have abandoned Atkins (bout of food poisoning after scoffing family-size chicken in one sitting), flunked FPlan and wobbled off Weight Watchers. Main exercise now - sporadic jogging and swimming apart - pulling cork out of wine bottle.

Still, retreat results promising (people dropping average 4.5lb and 2in off waist in week). Very much at home in fluffy white towelling robe and good at sipping orange juice, so will give it a go.

FRIDAY FEBRUARY 1
DAY ONE

This fitness business exhausting and not even out of London yet. Don't have half of things on "to bring" list so rush around Primark for 10 cheap polo-shirts, three pairs tracksuit bottoms, 10 pairs sports socks, etc, then mad dash to Paddington station. Missed breakfast as usual so pant into M&S for lunch to take on train. En route to till with egg-and-bacon sandwich but pop back for chicken pasta salad too. With rushing round, must have burnt enough calories to justify it. Feel thinner already.

Three hours later, Tiverton Parkway station, picked up by minibus from retreat. Bumpy ride along country roads, then arrive at old farm now turned into holiday accommodation. Can't see pool, but must be in huge shed over there.

Quick glance at room - clean, comfortable, en suite, but no mini-bar, and where is fluffy white robe? Squelch across farmyard for induction in dining room. No chairs, only big rubber gym balls. Squatting on them works core muscles, says health manager Julie Brealy. Yes, but will also crack skull if roll off.

Other 18 guests mainly women, but two men here to support partners, plus whippet-thin 18-year-old Dominic Beatson from Lincoln, here to encourage mum Lorna Micklefield.

The rules: no alcohol - gulp - or sneaky trips to village without retreat staff as chaperone.

Regime three meals a day, plus morning and afternoon snacks. Average 1,700 calories a day, but can ask for more if dizzy. Dizzy? Why? Soon find out. Average of six hours of exercise a day. What? When did agree to that?

Dinner (on chairs, at table, luxury) - grilled salmon with wild rice and curly kale, then fruit salad. Not bad. Settling down for nice relaxing night when all summoned to big shed seen on way in. Hope they are showing us spa pool and Jacuzzi. Greeted by Siân Cheedy, elfin Welsh women's football player and exercise coach for week. Bad news: this is "exercise barn". No pool, no Jacuzzi, and definitely no hoped-for secret cupboard of fluffy white robes.

Instead, huge red rubber mat on which will play team games. Now? Yes, now. Hour later, am done in. Was unexpected good fun but ready for bed and is only 9pm. Motivational signs pinned all over. "What Mind Can Conceive, Mind Can Achieve" etc. All mind can conceive right now is nice glass of red wine. If only.

DAY TWO

Up at six, weighed and measured. My targets: lose half stone; 3in off waist and 2.5in off hips; cut body fat 5 per cent. Resolved to achieve all, so attack next part of assessment - three-mile walk/jog through Devon countryside - at stupidly fast pace. Have to stop after a mile, wheezing, panting. By end, feel sick.

Minibus going back passes through Bampton village. "Look, a chip shop," says mournful voice. Faces press to window but back to farm for mid-morning snack of nuts and dried fruit. Before lunch, circuit training, then game in field, involving much dragging along of car tyres on rope.

Exhausted. Spoons on lunch table give rise to excited rumours of proper pudding but are for starter - miso soup. Tasty, but not cheesecake.