Mr & Mrs Much-Greener

The windmill has been taken down and he is cross. "It was a sweet little thing," says David Cameron within moments of opening the front door of his new eco-home in west London, "a lot smaller than a television aerial".

The mini-turbine was meant to be spinning by now, generating a trickle of electricity - and declaring the credentials of the leader of the new earth-friendly Conservatives. It was going to be a whirring banner for his environmentalism, the symbol of his personal righteousness in doing things like attack Tony Blair for making a carbon-guzzling "pop star" farewell tour of the world.

The plan went wrong, just as his abandonment of grammar schools threatens to go wrong. Some senior Tories are outraged that he thinks no more grammars should be built (a position he modified when their ire became clear).

The party's infighting over schools has damaged Cameron's standing as would-be Prime Minister. An ICM poll for The Sunday Telegraph today shows he is seen as a less capable leader than Gordon Brown. Former party deputy chairman Bernard Jenkin has described the row as "the first skid mark" of the Cameron era. But we are talking before all that, in the days preceding a family holiday in Crete that has taken him (with characteristic good fortune) out of the country during the worst week of his leadership. So it is not the wrath of Tory grandees that is on his mind but that of his local council.

"Somebody complained and it had to come down," Cameron says of the windmill in a mock sulk, making coffee in the open-plan kitchen and living room at the back of his house. The whole of one wall is made of glass, allowing early morning light to pour in from the garden. That's where the rainwater harvesting tank is buried.

His children are not even out of bed yet, but Cameron is dressed, in French blue, hair slicked back. I am the first interviewer to see him in the new-look house. It offers a tempting metaphor for his attempts to reinvent the Tories with the slogan "vote blue, get green".

From the outside it looks like other solid Edwardian terraced homes in his North Kensington street - apart from four alarmingly shiny metal bins. Inside, the white walls smell strongly of paint; pictures are propped up yet to be hung, including a poster for the Ingrid Bergman film Stromboli. All appears stylish and modern, just as the well-tailored 40-year-old Etonian would like us to see him. There are signs of humanity - his wife Samantha's party shoes lying on their side in the centre of a white rug - that even the controversial new party head of communications Andy Coulson (former editor of the News of the World) would find it hard to beat. The house is also stuffed with eco tricks - at least one of which does not work. "The windmill is sitting in my builder's garden," he says. "It was up for about a week." He had planning permission for it to go on one side of the chimney but the roof wouldn't hold it; so the builders put it on the other side - where there was no permission. "The architect advised me to take it down or be in breach, which wouldn't be right."

The windmill wasn't very good anyway, he admits. "We will apply again. We're still in the learning phase."

Cameron says that a lot. He takes credit for greening his party and putting the environment at the centre of the political agenda since he became Tory leader in 2005. "I believe there would not be a climate change Bill about to go into Parliament if it wasn't for us." Talking about what the Camerons do as a family supports that position. But it is also asking for trouble.

Some of his eco-failures and compromises have become infamous, others will only be revealed as we talk. But as we run through the details, from organic vegetables and solar panels to the 90-mile flight he took in a private jet, he keeps repeating that his family is just like many others. "We're all learning."

Talking about it too. His rivals have been reluctant to do so until now, but were prepared to tell this newspaper what they do. Menzies Campbell, leader of the Liberal Democrats, uses energy- saving lightbulbs and is having his car converted to run off LPG. Gordon Brown, Labour leader elect, has solar panels and a compost heap, takes the Tube "when he can" and has spent his last three holidays in Scotland. Both insist they recycle, insulate their homes and offset their official travel. A source close to Brown said, with irony: "David Cameron is clearly a model of how to live - and never misses an opportunity to tell us about it."

Brown and Cameron have both had to face challenges at home. David and Samantha's son Ivan, five, has epilepsy and cerebral palsy and needs round-the-clock care - perhaps the main reason for rebuilding the house - to provide him with the right facilities. They have two other children, Nancy, three, who pads downstairs as we talk and finds her father's lap; and Elwen, one, brought down by his mother to suck milk from a bottle on the sofa.