Close followers of Channel 4’s property show Grand Designs may have noticed that its presenter, Kevin McCloud, has been looking a lot healthier lately. He’s put on weight and he doesn’t need make-up on camera any more.

McCloud, 47, has finally found a remedy for the debilitating asthma he has suffered since his teens. For years he got by with a strict diet and standard Ventolin inhaler. But a year ago his asthma became dramatically worse, and he had to take six weeks off work. Eventually a colleague recommended John Costello, a consultant in respiratory medicine at King’s College and the Cromwell hospitals in London.

“He changed my life — he saved my life, actually. By the time I saw him I was extremely ill. I was stuck in one room all day with a dehumidifier or a humidifier, depending on how I was feeling, I had incredibly low energy and couldn’t do very much at all.

“He gave me a new drug, Symbicort (see below), which he told me many GPs are reluctant to prescribe because it is much more expensive than the average basic inhaler. Within a week I was outside smashing rocks. It’s as if my whole metabolism has woken up. I’ve have far more energy, I’ve put on two stone and my skin tone has improved — I used to be grey most of the time.

“I have to use the inhaler every day now; if I didn’t I would be in a box. I know there are issues with steroids but I will take as many drugs as I need if I can feel this healthy. I can exercise completely freely now and I have no symptoms at all. I don’t get asthma attacks any more and I don’t wheeze.

“I have had my truck with alternative therapies. I tried everything. I spent thousands of pounds looking for a solution, but none of them shifted the asthma. I used to follow this amazingly complicated complementary diet with no dairy, no wheat, no alcohol. I didn’t drink for 15 years because of my asthma. Now I buy bottles of vintage claret to make up.”

McCloud, who lives with his wife, Zani, and four children on a farm in Somerset, is one of television’s less likely pin-ups. It’s thanks to him that Grand Designs, a programme about people building their own houses, has consistently attracted audiences of more than five million since it was launched in 1999. He is a genuine, well-informed enthusiast with a dry wit: he studied history of art and architecture at Cambridge and ran his own design business before he became involved with television.

Grand Designs is the acceptable face of reality TV: it offers up plenty of highly entertaining barneys between builders and clients and neighbours, plus opportunities to envy or disapprove. And although the participants are at the mercy of McCloud’s polite put-downs, as in: “I’m not entirely convinced that this is one of Katrin’s most sensible ideas . . .” you never feel they are being manipulated.

McCloud claims that his favourite Grand Designs projects are the less flashy, eco-friendly houses with plenty of personality. That may be so, but there’s no concealing the admiration in his voice when people install state-of-the-art lighting systems or spend thousands on individually-tailored stairtreads.

This is the classic conflict of modern life, squaring the opposing demands of everyday life, and the things we can’t help loving, with doing one’s bit for the environment. McCloud is genuinely evangelical about sustainable living, but he is also passionate about cars.

He has three: a Land Rover, a Saab 95 and a little sports car, all of which run on alternative fuel, plus a collection of model cars in his office at home: “I love looking at them. They are the most exquisite things.”

He blames his passion on his father, an engineer. From the age of six McCloud spent Sunday mornings with his father tinkering under the bonnet of their car. His father built the family house in Bedfordshire. One of

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