It is quite amazing what some people will believe. People who should really have enough sense — or at least enough money — to know better.

Take, for instance, the followers of Dr Deepak Chopra. Chopra is a real doctor whose credentials, like his powers of reason if not his bank balance, have lapsed. He makes millions of dollars by advising the gullible. His bestsellers, among their many banalities, take literally the maxim that age is a state of mind. “People grow old and die because they have seen other people grow old and die,” he argues. “Ageing is simply learned behaviour.”

It hardly takes a genius to spot the flaws. Yet Chopra’s speaking fee is $25,000 (£13,600), his annual income tops $20 million and his list of client-disciples includes Madonna, Hillary Clinton and Mikhail Gorbachev.

Demi Moore hopes to live to a great age through his teachings. “Even 130 years isn’t impossible,” she says.

Modern peddlers of snake oil such as Chopra are the worthy targets of a coruscating new book: Francis Wheen’s How Mumbo-Jumbo Conquered the World. From Ronald Reagan’s astrological charts to Cherie Blair’s “BioElectric Shield” and the Queen and her heir’s homeopathic hokum, it lays bare the extent to which delusion, paranoia, ignorance and nonsense have takenover public life.

Far too many otherwise sensible people, Wheen argues, have abandoned rational inquiry for superstition, instinct and anecdote. As he puts it: “It was as if the Enlightenment had never happened.” This flight from facts has appeared in many guises. Creationism and postmodernism, alternative medical quackery and management speak are all cut from the same cloth: they share a pig-headed refusal to face up to sober evidence that the emperor is wearing no clothes.

Then there are the campaigners who insist that GM crops will poison you, that the MMR vaccine will make your child autistic, or that the Pill and abortion will give you cancer. No place here for balanced assessment of

the best available data. It’s decision by emotion and

gut feeling, and never mind

the science. All this leaves us not just intellectually but materially poorer. Leaving aside the public-health consequences of unfounded scares such as MMR, the indulgence of mumbo jumbo and anti-science creates

misplaced doubt about who and what to trust.

A relativist approach to

truth makes it easier than

ever for charlatans to target the vulnerable. Cherie’s predilection for crystals and Mayan rebirthing barely dents her salary. But one of the most alarming findings of last month’s Body&Soul research into complementary medicine was that the poorest social groups spend the biggest slices of income on it.

Wheen’s assault on the pomposity and folly of the reason-free zone is important and timely. But there were interesting signs this week that the public is also starting to come to its senses.

A MORI poll for Nature and the Science Media Centre found that hardly anyone understood the concept of peer review — the independent refereeing process for scientific

research.

But when asked how they wanted experts to behave when in possession of explosive research about a risk to health, a massive majority wanted something very similar.

Some 30 per cent said that the work should be checked by independent experts before it is released to the media. Even more — 41 per cent — wanted the results independently replicated. If peer review did not already exist, it would probably be necessary to invent it.

This is encouraging stuff. More encouraging still is the news that MMR vaccination rates have finally started to rise again, after a couple of years in which they have been driven ever lower by the irresponsible and misguided campaign against the vaccine.

The values of the Enlightenment may be fighting back after all. “Truth is great and will prevail,” Wheen concludes — and he’s right: how many people today think Galileo took the wrong side? But the idea that facts and evidence are sacred was hard won — as Galileo and others discovered. The modern world loses sight of it at its peril.

Mark Henderson is The Times science correspondent