WHAT kind of doctor is James Colthurst? He is not entirely sure. “A curious doctor,” he suggests. He does not use the words alternative or complementary, though others would. His approach is integrated, he says, combining the best of conventional methods — he used to be a surgeon — with anything else that might solve the problem. This includes “stirring the spirit”, and “helping people to help themselves”.

Common sense, you might say. Yet it is not part of mainstream medicine to ask people why they think they became ill, to suggest that they might benefit from surrounding themselves with positive forces, with friends and acquaintances whose presence makes them feel better. Colthurst believes it should be. Hence his book, Cancer Positive, in which he advises people who are ill — his tactics are also applicable to those with other conditions — to shake off destructive patterns of behaviour and find a new positive focus in their lives. He is not saying don’t have chemotherapy, but suggesting that there is value in acknowledging wellness, rather than looking only at past, existing or potential illness.

“I’m not talking about people smiling inanely and saying ‘I’m now thinking positively’,” he says. “But it’s helpful if people have something to base positive thinking on, and actions to take. I like to make people aware that there are tools around them and if they use them, they may get a different view. I believe a lot of so-called recurrence happens because the state of mind has not altered. They’ve been through treatment and the same triggers are there when they emerge.”

As evidence that a positive focus can stave off recurrence, he cites case histories: the patient who took up parachute jumping, the estate agent who set up his own business. It is worth remembering, too, that he had one friend whom we can assume benefited from his upbeat demeanour: Diana, Princess of Wales. For a brief period after her death, Colthurst was infamous as the man who acted as a gobetween, ferrying tapes, in which she exposed details of her marriage to Andrew Morton.

Why did he become involved in an undercover operation to feed someone else’s book?

“I think medics help: if you’re asked to help, you help,” he says. “It’s not always welcome to yourself or those around you. It’s not always easy. But if you believe it’s important to them, that’s what happens. If you feel someone’s batteries are down, you want to lift them. Diana’s batteries were down then. It was a difficult time.”

He treated the Princess for coughs and colds, he says, though when I ask about her bulimia and suicide attempts he says patient confidentiality prevents him from commenting. They had met on a skiing holiday when she was 17 and he was a medical student. He comes from a noted Irish family and had been to Eton, he is warm and amiable, and it is easy to understand why she liked him, although they were never romantically involved, he says. “I was quite direct with her. There was a lot of sycophancy around; maybe it was easier to have someone occasionally call a spade a spade.”

It was his idea that rather than deliver a supplied speech to an organisation of which the Princess was patron, she should deliver her own. “I said if you have a view, why not use that and give a speech you’re interested in delivering? Delivery wasn’t always her strong point; nonetheless, she found it attractive to make some points, so we had good fun cobbling them together. That’s maybe what she found fun. It was nice to see someone get a lift. She was by no means dumb and it was nice to see some of the perspective she had being put across in a different way.”

So he regards himself as one of her support team. “She had plenty of others and they blew hot and cold and she blew hot and cold. I lost touch for the last couple of years. People who are very close at one moment in someone’s life are not necessarily the best suited to deal with the next moment. It’s important for people to move on and not attach like limpets.”

Ten years ago, after suffering Lloyd’s losses, Colthurst left hospital medicine — he was about to become a senior registrar — for a business degree at Henley Management Centre. He later became the first surgeon since 1947 to train in homoeopathy, and set up his own private practice in Hungerford, which is where we meet. He is 45, married, and has two daughters.

He admits that he left mainstream medicine partly because of financial problems, but he had also become frustrated by the inadequacies of hospital practice: too much emphasis has been put on equipment, and not enough on training staff to encourage patients to see their illness in the context of their lives. The result is often an inflexible system that fails patients, he says. “The machine element of medicine is strong. The patient becomes a number and a code and that’s their illness and their identity in the system. The label may not fit, but in the interests of financial management for the hospital you have to have a label, otherwise you can’t be categorised. You then get evidence-based treatment for a label that ill fits you, then you don’t perform, and become an atypical responder.

“With the integrated approach, you recognise that there are several issues that may be helped, and maybe on the basis of a couple of per cent improvement on each thing you can get a worthwhile change.”

Colthurst’s point is that every patient is different, and that human beings are better at assessing their vagaries than machines. He cites hospital admission systems: experienced nurses can best ensure high bed occupancy because they know about patients’ home circumstances, and when they can go home, “a calculation a computer can’t make”. Similarly, he believes that the system of regularly spaced outpatient appointments encourages patients to think of themselves as being ill. Much better, he argues, to drop them, as he did, ensure that they have good GP support, and guarantee that patients can see a hospital doctor when they need to.

How do mainstream medics react to him? “I think they’re glad that there may be other aspects of things that they’re not taught to handle. The tools we’re given in hospital may not be enough. The idea of self-support is seen as alternative soft stuff, but it’s not conflicting with doctors, it’s mainly raising patients’ awareness.”

Cancer Positive: The Role of the Mind in Defeating Cancer is published by Michael O’Mara Books on July 7, £9.99. Available from Times Books Direct for £8.49, plus 99p p&p: 0870 160 8080; www.timesonline.co.uk/booksdirect

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