The sclerotherapy drug used will be Sodium Tetradecyl Sulphate, also known as STD and marketed as Fibrovein® (STD Pharmaceutical Products, Hereford, UK). STD comes in different variations of concentration, for this trial we will use 3%, 1.5% or 1% STD depending on the procedure protocol. STD can be used as foam or as a liquid preparation which makes it ideal for our study. The STD used will be from routine stocks. It will be stored at room temperature in a suitably secure location in the ward, clinic or theatre. Careful records will be kept regarding which participants receive STD and its batch number Preoperative procedure The treatment aim is to eradicate any significant SVI present in the limb. Preoperatively the veins are marked by the surgeon using duplex-ultrasound with the patient standing. This will identify the extent and position of the refluxing axial vein alongside any incompetent perforating veins and varicose tributaries. The significant superficial varicose vein (GSV, ASV, SSV, GV) to be treated will have its length measured and noted. In addition, the average diameter of the varicose vein will be calculated via three transverse images of the vein (proximal, middle and distal) and noted. Potential areas to be punctured by cannulae may have local analgesia applied prior to treatment. The participant will be positioned supine on the operating table where in the Clarivein and Ultrasound Catheter group sterile precautions including disinfectant skin preparation and sterile draping will be employed, and the Foam Sclerotherapy and tributary treatment group skin disinfectant only. The ultrasound transducer will be prepared with a sterile covering and secured to the sterile drapes to allow sterile intra-operative ultrasound duplex scanning.