Asbestos is a dangerous substance that was widely used in building materials in the past, including roofing, insulation, and ceiling tiles. It was used due to its insulating and fire-resistant properties. While the use of asbestos has been banned in the UK since 1999, it is still present in many buildings constructed before that time. Exposure to asbestos can lead to serious health conditions such as mesothelioma, lung cancer, and asbestosis.