This is a clinical trial investigating the effectiveness and safety of the combination of the study drugs cetuximab and erlotinib in patients with advanced (metastatic) refractory colorectal (bowel) cancer. If bowel cancer has spread to other organs (metastatic colorectal cancer), it is usually incurable and life-expectancy without treatment is less then 6 months on average. Currently, chemotherapy has been shown to have a significant impact in advanced colorectal cancer in terms of maintenance of quality of life and extension of survival. However, ultimately tumours will develop resistance to chemotherapy. Treatment options and subsequent survival at that stage are very limited. Therefore, new therapeutic approaches are urgently needed.