Design A single case experimental design (ABACADA) will be used. A, B, C etc represents points of intervention and clinical contact with participants when standardised outcome measures will be administered by the treating clinician at each session. Phases A1, A2, A3 represent time between contact during which participants will undertake daily monitoring of idiosyncratic symptoms on Visual Analogue Scales (VAS) e.g. degree of avoidance, degree of worry, degree of nausea etc, so change between phases across time can be measured.