24th century

In about the 24th century, London ceased to exist as a distinct geographical and political unit. It was absorbed into a greater metropolitan area that — by the 28th century — was called Central City. (TV: "Strangers in Space")

Also this century, humans discovered the planet Solos, colonised it, and started to exploit its inhabitants, whom they mistakenly believed to be "primitives". (TV: The Mutants)