Prince Charles will claim that chronic illnesses like diabetes and heart disease which affect tens of millions worldwide could be successfully treated by using complementary medicines and a "whole body" approach to healthcare.

His comments, which will invite complaints from his critics, are to be made in a keynote address to the WHO's annual assembly in Geneva on 23 May where the prince will set out his case for "integrated healthcare" to a global audience for the first time.

The prince is expected to argue that doctors should put less reliance on conventional drug-based treatments and take a more "holistic" view by putting greater emphasis on preventative healthcare, improving diets and tackling unhealthy lifestyles.

This would help tackle endemic conditions such as stroke, heart disease and diabetes which kill 35m people worldwide a year, he will say.

The prince also believes there is proven evidence that some mental illness can be treated successfully without using anti-depressants, such as the herb St John's Wort and baby massage for post-natal depression.

Doctors and governments should be focusing on diet, environmental pollution, and reducing the use of harmful chemicals in homes and farms.

In a speech last year when he was made an Honorary Fellow of the Royal Society of Medicine, Prince Charles said modern, western lifestyles played a major role in the rise of allergic diseases such as asthma, various cancers and in obesity.

"The human body has too often been mechanistically reduced to individual parts and treated with limited reference to the whole person, " he said then. "The time is now right for a fundamental reappraisal of the way in which we view healthcare: quite simply, it is surely time to adopt a far more holistic approach to health."