This has to be the wrong house. Not just the wrong house, but the wrong street. The wrong street in the wrong town. I have followed directions to the School and Clinic of Electro-Crystal Therapy, and the trail has ended in the west London suburb of South Ruislip.

School? Clinic? Number 117 is an inter-war semi, just like all the others. But the American woman who answers the door is expecting me. “I’ll tell Harry you’re here,” she says, then disappears into a suburban kitchen to boil the kettle.

I’m sipping coffee on a chair at the foot of the stairs and reading an unobtrusive text on the wall about the relevance of Jesus today, when Harry Oldfield appears from the lounge. He is friendly and very polite, wears a white shirt without a tie and sandals without socks. Who does he remind me of? A cuddly Paul Merton perhaps? If South Ruislip has taught me one thing already, it is that appearances count for nothing.

Take the lounge. At first glance it like any suburban lounge. The television is only slightly larger than might be expected, and the display of quartzon the radiator shelf could haver been assembled by any hill walker with an eye for rocks. But the young woman in the armchair - what on earth is she up to?

Around her head is a Dr Who device comprising a transparent plastic tube filled with clear liquid. The liquid - it turns out to be brine - contains dozens of coloured crystals, and the entire gizmo (she has another around her middle) is connected with leads to an electrical control box.

“Lynn,” says Harry, “is receiving alpha rhythms.” And he explains how the frequency of 7.8 cycles per second crops up time and again in the natural world, from the deep resonances of the Earth itself to the contented purring of a cat.

Harry, it has to be said, is not purring today. This has nothing to do with having swapped teaching at a London secondary for a career in complementary medicine - he made that choice almost 20 years ago, and despite some fond memories (“tears sometimes well up in my eyes when I smell floor polish”) it was clearly the right move. What’s giving him bad vibrations is the fact that his printer doesn’t get on with his scanner.

While he slips out for another anxious chat with the man who’s come to reconcile his software, I concentrate on that over-sized TV screen. A Sky programme, recorded a few years back, will be the best introduction to his work, says Harry. So I sit back to watch.

Here is a man who was paralysed and blinded by a brain tumour, until Harry got cracking with his crystals. Here is a woman diagnosed with breast cancer. Today, after a course of therapy (two sessions a day for as long as it took), she is fit and well. And there are others - each, perhaps, a living testimony to the potential of electro-crystal therapy.

Finally there are the remarkable scans: computer images of Harry’s patients generated by a hand-held sensor not unlike a photographic light meter. What they show us, with the aid of computer processing, is something only certain people claim ever to have seen before - the human aura. And not just the existence of the aura, but its texture. its highs and lows, its strengths and its weaknesses, all picked out in rippling rainbow colours. It is these ever-changing maps of the human energy flow that Harry uses in his electro-crystal therapy.

“We use energy to treat energy,” he says, returning from a depressing conversation in the next room, The different parts of the body vibrate at different frequencies, and what we’ve worked out is the way to contact these zones. We know the frequencies that stimulate, that balance and that tranquilise. And we’ve made our electromagnetic units to pulse at these frequencies.”

He indicates the device to which Lynn is contentedly connected. “At the end of our tubes,” he says, “we have crystals - natural tuning forks - which have intrinsic healing properties. And when they’re stimulated with electromagnetic waves, they correspondingly release those healing properties to the body.” He talks about the chakras, meridian lines and acupuncture points that Eastern medicine has charted for thousands of years. “The ancients knew to wear jewellery, not just for adornment, but for building up their own energy fields for certain religious or psychic or energetic purposes.”

And in the same breath he cites voltages and frequencies and all the paraphernalia of Western learning. I remember then, for it’s easy to forget, that Harry the Healer was once Mr Oldfield the science teacher. “Physics and biology,” he says. “I taught all over the place as a supply teacher. But from the mid-Seventies to the early Eighties, I was at St Edmund’s in Fulham Palace Road.”

And it was while running his popular after-school science club at St Edmund’s that Harry first came across Kirlian electrography, a Russian technique that produced images on photographic paper of invisible energy fields. Those images were to change his life. For the past 20 years he has been developing the technique to a stage where it can detect and depict the subtle forces he believes are the templates of all living organisms.

One product of this work has been the development of a new way of viewing micro-organisms; mainstream science is now showing an interest in the Oldfield Enhanced Microscope System. Another has been the clinic, and yet another the school (he teaches 20 or 30 people a year the theory and practice of electro-crystal therapy).

The time has come for my scan. We enter a back room that until now has been occupied by a woman who walks slowly and painfully with an aluminium frame. “If you spot anything nasty,” I tell Harry, “I’d rather not know.” But he assures me it won’t be like that, stands me in front of a white surface and makes me relax as one of his students pans the scanner across my face. This is the “before” shot.

Now, he says, he wants me to concentrate hard on something that will make me stressed. I’m spoilt for choice. “You won’t cheat?” he says. But now it’s my turn to reassure him. And, suddenly, there it is on the monitor - a concentration of dark blue above my right eye.

“Can you see that?” asks Harry, pointing at the monitor. It is, he says, a very clear example. A shame he can’t print the images, but as soon as the software’s fixed he’ll send them to me.”

Watching him there, beaming at the screen, twiddling knobs and adjusting frequencies, it’s not hard to see why the kids at St Edmund’s stayed behind after school to learn more about science. Enthusiasm, it seems to me, is one energy field that can be detected without any electronic aid whatsoever.