Some 200 years ago, William Blake, an obscure and eccentric London engraver, wrote and illustrated “Milton: A Poem.” In its preface, later adapted to become a popular hymn, he evoked the ancient legend that Jesus Christ once visited England, and called for a new Jerusalem to be built “in England’s green and pleasant land.” The phrase, as simple as it was apt, has stuck in the national memory.

But Blake could not have foreseen how two centuries later an alliance of fanatical activists and political opportunists would conspire to give an entirely new meaning to “green” — one which now threatens the liberty and prosperity that used to make England such a pleasant land. Indeed, Britons are witnessing a bizarre bidding war between politicians, each desperate to prove that he is the greenest of them all.

On Tuesday, Tony Blair unveiled his draft Climate Change Bill, which he claims will be the toughest in the world, before an audience of teenagers. Not to be outdone, his Conservative rival, David Cameron, spoke of “opening up a second front in the green revolution” and boasted of his part in promoting “greener skies” — which sounded like a schlock science fiction movie.

The campaign to stop global warming resembles nothing so much as the student movements of the late 1960s, which many of our political leaders fondly remember from their youth. Like the green revolution today, the cultural revolution that followed in the wake of the student movements also seemed to sweep all before it. Grown-up statesmen pandered to the narcissistic “hang-ups” of a pampered younger generation — the same generation that is now falling hook, line, and sinker for the dubious theory that global warming is caused by man-made carbon emissions.

Actually, it is getting harder to tell the difference between the grown-ups and the teenagers. On Monday, Mr. Cameron claimed that the “carbon budget,” when the government will report annually on its progress in meeting targets to cut emissions, would soon be as important as the regular budget. This is the politics of the campus, not that of the mother of parliaments.

Climate change is probably not even the most urgent of the environmental problems that any government must deal with — let alone all its other responsibilities. To prioritize a single issue to the exclusion of other less fashionable but more important ones is unworthy of a prime minister-in-waiting.

Superficially, the global warming panic is driven by scientists. But the boom in climatology has been funded by taxpayers’ money — and he who pays the piper calls the tune. Nobody who needs research funds dares to question the consensus. Nevertheless, a few scientists persist in their skepticism. At the same time, attempts to stifle dissenting scientists have become ever more extreme, from professional ostracism to death threats. A Canadian professor, Timothy Ball, has received five such threats.

Even the Holocaust has been enlisted — and trivialized — in the cause: in the scale of environmental crimes, “global warming denial” is on a par with genocide. The next report of the Intergovernmental Panel on Climate Change — the Bible of the global warming lobby — is being rewritten to ensure that the facts fit the theory. One of its pioneers, Mike Hulme, founder of the Tyndall Center for Climate Change Research, wrote yesterday in the Guardian, “Climate change is too important to be left to scientists — least of all the normal ones.” Precisely.

Last week saw a rare challenge to this ideology, when Channel Four broadcast “The Great Global Warming Swindle,” which included contributions from several distinguished scientists and Margaret Thatcher’s most brilliant minister, Nigel Lawson.

It took just 90 minutes to persuade my very green 15-year-old daughter not only to re-examine the evidence that human carbon-dioxide emissions are to blame for global warming, but also to consider the retrogressive impact of green policies on the poor.

When asked about this film, the environment secretary, David Miliband — widely seen as a future prime minister — said, “I didn’t see the programme — but I promise you I will do a blog demolishing its contents.” At the time of writing, he hadn’t yet made good that promise.

David Cameron did not even bother to comment. The Tory leader is forcing his team to endure a seminar with Al Gore — a cruel but alas no longer unusual punishment.

What really spooks me is the way in which even very young children are indoctrinated in what amounts to an allembracing pseudo-religion. On Tuesday, two of my children, ages 9 and 12, joined 1,200 other children taking part in a spectacular performance at the Royal Albert Hall of “Ocean World,” an environmental oratorio.

The music was very exciting, but the underlying message — humanity will poison the oceans unless it is stopped — was all the more disturbing because it was delivered with such power. However intoxicating for its votaries, environmentalism offers a bleak view of the world, and a devilish one of mankind. “Into the dangerous world I leapt,” Blake’s child exclaims in “Songs of Experience,” “like a fiend hid in a cloud.”

Our infants are learning that clouds are “greenhouse gases” and we are all fiends.