In the 1950s and 60s, British scientists secretly released harmless bacteria in London’s Underground to study how biological agents could spread

For several decades during the Cold War, British government scientists carried out a covert program testing how biological agents might spread through crowded public spaces, and the London Underground became one of their test sites. Researchers linked to the Microbiological Research Establishment at Porton Down dropped small containers of bacterial spores from moving trains and released organisms in station tunnels, then tracked how far the material travelled and how long it lingered in the air.

Raccontata datimesofindia.indiatimes.com