He looks unsustainably glamorous for an environmentalist: has he been genetically modified? Tanned and pin-striped with his father Jimmy’s mesmerising eyes, Zac Goldsmith appears more like a film star in the bar of a Mayfair hotel than the next Swampy. Little wonder, as one of the leading campaigners against nuclear power in Britain, he is gaining new friends.

“I didn’t know if you were interviewing me or someone else, so I approached a woman and asked if she was from The Sunday Times,” he smiles sheepishly. “She said ‘yes’ and let me burble away about environmental destruction for 10 minutes. It was hardly the most obvious seduction line.”

Actually, the lines he has been spinning in television studios sound mighty appealing: while Conservatives, and even conservationists, have rolled over in the face of Tony Blair’s determination to go nuclear, Goldsmith insists there is an alternative. And while an earlier generation of those who chanted “no nukes” were absolutist, Goldsmith is engagingly honest, admitting there are trade-offs: it is tricky being green — even if your bank account bulges as far into the black as Goldsmith’s; he is, after all, heir to the late Jimmy Goldsmith’s squillions.

“I was a chain smoker until four hours ago and now I am reduced to chewing these,” the 30-year-old laughs, tossing an empty pack of Nicorette into the ashtray “and I have just discovered they are made by Monsanto, one of my least favourite companies.” And boosting profits of the genetically modified food monster is not his only compromise. “I keep telling people, ‘Please don’t bring these hideous plastic toys for my children into my house’. They have ‘landfill’ written all over them.”

Before I can venture that Christmas chez Goldsmith with his wife Sheherazade and their three children sounds light on fun, he concedes: “Equally, I don’t want my children to be the fruits just because they are the only ones without toys.” How careful is he — one of the most privileged humans on the planet, the beneficiary of a singularly ruthless form of capitalism — to ensure his investments are ethical? “Investments are bets,” counters the poker enthusiast, “and I only bet on what I want to happen. But I have money in banks. I would not claim to be a model of ecological living. Society makes rampant consumers of us all.” Or rather: we all make society rampantly consumerist.

Going without is hardly a typical Goldsmith pastime. Having made a pile from Ambrosia Cream Rice and much else beside, Jimmy married his former mistress, Annabel, inspiration for Annabel’s nightclub. Zac’s sister is the equally glamorous Jemima Khan, former wife of Imran Khan and sometime armrest of Hugh Grant.

Still, most of us harbour hypocrisies. And Goldsmith can’t win: if he frittered all his days in casinos, a playboy re-creating his father’s Clermont set, those who attack him for presuming to know about the planet would accuse him of fecklessness. Goldsmith, who owns and edits The Ecologist magazine, is eager to show he has done his research, gabbling about green stuff with the speed of a true believer. And he is compelling. He asserts we could save 40% of our energy use “without living like monks or even tightening our belts”, which sounds incredible until he gives examples. “We could use light bulbs that last nine times longer,” he says. “Or I have it from the horse’s mouth that a supermarket flies British apples to South Africa to be waxed, and then flies them back. And it is a fraud because the purpose is to give the apples the appearance of freshness.

” He holds his hands to the heavens.

But just because it is mad it does not follow that it can be stopped. He complains that Britain and the Netherlands buy the same number of chickens from each other, wasting transport fuel. But if you believe in free markets — and Goldsmith has been accepted as a Conservative parliamentary candidate — then how can he complain? He advocates a levy on aviation fuel, particularly on cargo planes, but Labour — and Tories — fear this would hit trade. “There are

people in the Conservative party who are not conservatives; I call them radicals. But the party has no identity at the moment, it is thrashing around. There is an opportunity to reshape the party.”

Yet the days when Tories wanted to preserve an essence of Englishness have long gone; they pioneered the motorway network and out-of-town shopping centres. Goldsmith takes the point, though he says Labour “made the best case ever against road building but is now building as many as when Swampy campaigned against Conservative road building”.

But if David Cameron is passionately opposed to nuclear power he has kept it clasped as tightly to his chest as all his other policies. “I don’t know what he thinks about it,” Goldsmith concedes of his prospective leader. “I suspect on this I am in a serious minority.” That does not make him wrong. He laments the loss of a bill in America making cars 5% more expensive but 20% more efficient. “The saving,” says Goldsmith, who claims to drive a five-year-old Volkswagen Golf, “would be the equivalent of all the oil America imports from Saudi Arabia.”

He is surely right that governments should do more to make energy savings and encourage us to do the same; but surely we should have evidence that we are really saving energy before we gamble our futures on it? And as our economy expands, we might find we need even more energy. To say “no” to nuclear is to take a leap of faith. It is not necessarily silly, but it is risky.