The Manhattan Project.
Valley Works, in the countryside west of Mold in North Wales, was developed in the late 1930s as a shadow factory for Imperial Chemical Industries (ICI) Randle Works in Runcorn, where mustard gas was made. (We developed and maintained a viable stock of weaponised mustard gas for use on Britain’s beaches should a Nazi German invasion have been attempted. The anti-invasion preparations undertaken in 1940-41 were part of a now iconic period of British modern history. ICI Widnes/Runcorn made a direct, but not well-known contribution to maintaining British sovereignty. A last-ditch area denial tool in case of a Nazi German invasion and following D-Day when the capability was used to counter the perceived threat of dirty uranium warhead-equipped V rockets).
In 1941, the MAUD committee reported that an atom bomb was theoretically possible, and it was decided to start work on the formidable task of separating uranium isotopes.
British wartime nuclear weapons program established a pilot plant to produce uranium hexafluoride in Widnes.
ICI also explored methods of producing pure uranium metal.