The evolutionary biologist and best-selling author of The God Delusion will appear as a guest star in the new series of Doctor Who, which began last night.

Gwyneth Paltrow threw down the gauntlet to "evil genes", Stella McCartney compared skin lotions to antifreeze, and the television presenter Sarah Beeny spoke on screen about chemical-free make-up. Now the scientific claims of the celebrities who appear on our television screens with advice on living healthy lifestyles and avoiding toxins have been put under the microscope.