Participants judged to be at high risk of venous thromboembolic disease (VTE) due to the use of exogenous oestrogens, past medical history or a family history of VTE or thrombophilia or immobility will be given a single pre-operative dose of prophylactic molecular weight heparin (LMWH), in the absence of contraindications. All participants will have duplex assessment and marking using the same protocol with only the endovenous procedure differing.