There is a growing trend to remove lung metastases with an operation, in the belief that this will help patients live longer, however there have not been any scientific studies to prove this. There is also very little published information about the side effects of this surgery and how it affects subsequent daily living. This is a feasibility study to determine whether it will be possible to conduct a large randomised controlled trial investigating the value of pulmonary metastasectomy (surgery to remove lung metastases) in patients who have been successfully treated for colorectal cancer. There is a two stage consent and randomisation process. Firstly, patients will be invited to consent to having a full range of investigations to assess their suitability for surgery. If found to be suitable, they will then be invited to consent to randomisation between active monitoring of their disease or active monitoring with pulmonary metastasectomy. Patients will be followed up regularly for 5 years to assess their disease status and to measure their quality of life and lung function.