Alexander Fleck began his career in the laboratory of Frederick Soddy, Nobel laureate in 1921, where Fleck studied radioactive elements and Soddy later emphasized that it was Fleck’s research that provided the final proof of the correctness of his theory of isotopes. This led to Fleck being made a Fellow of the Royal Society.
In 1920, he was appointed director of the United Alkali Company. His research interests at this time were in chemicals that could be used in agriculture. In 1926, several companies, including the United Alkali Company, merged to form Imperial Chemical Industries (ICI), which remains one of the world’s largest chemical companies.
In the 1950s, Fleck also worked for the British government. He was commissioned by the government to compile a comprehensive survey of the research activities of the coal, gas and electricity industries so that they could be better coordinated in the future.