The risk of unexploded ordnance on construction sites in London, UK

Greater London, UK, among many large cities, was subject to bombing by the German military in both the First World War and Second World War (WW2) and was the target of many air raids during WW2. This was particularly the case during the Blitz, September 1940–May 1941, when over 28 000 high-explosive bombs and parachute mines were dropped on London. Post-war research conducted in 1949 estimated that approximately 12 750 t of bombs, including V1 and V2 rockets, were dropped on London. The night of 16–17 April 1941 was one of the worst bombing raids, when 446 t of bombs were dropped on London and over 58 t did not detonate. Unexploded bombs remain buried underground today, as they were unidentified at the time or abandoned owing to difficulties in recovering them. Uncharted bombs continue to pose a potentially significant hazard for developments around London. This paper considers the probability of discovering unexploded ordnance (UXO), particularly WW2 ordnance, during intrusive groundworks in London. The prevalence of UXO has been assessed using data obtained from governmental organisations to estimate the likelihood of discovery in London.