In  Comrade Haldane Is Too Busy to Go on Holiday: The Genius Who Spied for Stalin, Gavan Tredoux provides extensive proof  of Haldane's espionage and collaboration with with Russian Communism during the Cold War:

https://book4you.org/book/5026292/e829d2

Samanth Subramanian, author of this book, seems to approve.

A biography of J. B. S. Haldane, the British scientist, philosopher, and rabble-rouser whose innovative predictions inspired Aldous Huxley's Brave New World.

J. B. S. Haldane's life was rich and strange, never short on genius or drama. He's best remembered as a geneticist who revolutionized our understanding of evolution. His peers hailed him as a polymath; one student called him "the last man who knew all there was to be known." He foresaw in vitro fertilization, peak oil, and the hydrogen fuel cell. He was also a staunch Communist, which led him to Spain during the Civil War and drew suspicions that he was spying for the Soviets. He wrote copiously on science and politics in newspapers and magazines, and he gave speeches in town halls and on the radio—all of which made him, in his day, as famous in Britain as Einstein.

A Dominant Character recounts Haldane's boisterous life and examines the questions he raised about the intersections of...