My sincerest and heartfelt thanks go to the following people without whom this work would never have been completed:

• My supervisors Tim Bishop and Paul Finan for all their support and sound advice.
• The 'FlexiScope Girls', Angela Butler, Joyce Pearson and Sue Corcoran and the staff of the endoscopy unit at Leeds General Infirmary who were so enthusiastic and hard-working.
• Julie Miller, the FlexiScope trial administrator, who was invaluable and without her I am sure the organisation of the trial would have failed.
• Juliette Moore, Rupert Gaut and the other scientists and laboratory staff of the Cancer Genetics department of St. James's University Hospital for tolerating a surgeon in their midst.
• All the staff of the Cancer Research U.K. Genetic Epidemiology department at St. James's University Hospital for their help and support.
• Jenny Barrett, Faye Turner and Rob Edwards for their amazing ability to instil some statistical understanding to a simple medic.
• The FlexiScope Trial team headed by Wendy Atkin without whom there would have been no basis for this research.