This is a feasibility trial designed to test the feasibility and acceptability of a one-day Cognitive Behavioural Therapy (CBT) workshop intervention ("DISCOVER") for young people aged between 15-18 years, who are on local child and adolescent mental health services (CAMHS) waiting lists, awaiting treatment for difficulties with anxiety and/or depression. Participants will be randomised to receive either the DISCOVER workshop (in addition usual care) or to continue usual care.