A modular containment system allows an enclosure of almost any size and shape to be assembled quickly and easily, using standard panels made from fire-retardant Glass Reinforced Plastic. The modular construction can incorporate entry/exit areas with change and shower facilities; ports for material ‘posting’ and services; windows for viewing and lighting; mobile ventilation / filtration systems; and lifting equipment. It provides a very effective and versatile containment to prevent the spread of contaminants during intrusive works.