What causes cancer -and how is it caused? Some people are convinced that vast numbers of people die from cancer contracted at their work place as a result of environmental factors such as synthetic chemicals. As a result of this belief, trade unions are exerting powerful political pressure to force industry to improve its safety standards. But what are the facts? If we could understand how cancer is caused, not only could we find out whether these worrying claims are correct, but we could also prevent cancer. In this programme two courageous men, jump jockey Bob Champion and sea captain Arthur Wilson, discuss what they know of the origins of their cancers-and the consequences. Written and narrated by ROBERT REID Assistant producer LESLIE NEWSON Producer PETER SPRY-LEVERTON