Although he identified with Communism he never joined the Communist Party of Palestine as he never met any of its members prior to becoming a socialist activist. However he did join a Zionist Socialist group and in it became both a Trotskyist and a confirmed opponent of the Zionist project. After becoming a Trotskyist in 1933 he was involved in leading groups until his death in 2000.
During World War II, Cliff was imprisoned by the British authority then governing the territory. After his release, he moved to Britain in 1947, but was never able to become a citizen and remained a stateless person. He was for a while deported to the Republic of Ireland and was only permitted to take up British residency due to his partner's status as a citizen. On his return to London, he again became active with the Revolutionary Communist Party onto whose leadership he had been co-opted. On the break-up of the RCP, he briefly joined Gerry Healy's group The Club, but was soon expelled because he assessed the Soviet Union as being state capitalist.
In 1950 he helped launch the Socialist Review Group which was based around a journal of the same name. This was to be the main publication for which he wrote during the 1950s until it was superseded by International Socialism in 1960, eventually ceasing publication altogether in 1962. The group was renamed the International Socialists at the same time and was to grow from less than 100 members in 1960 until it claimed in the region of 3,000 in 1977, at which point it was renamed the Socialist Workers Party. Cliffs biography is, as he himself remarked inseparable from that of the groups he was a member of.
Cliff was a prolific author and journalist. His works were published in many languages as a result of the international nature of the movement of which he was a leader. A list of some of the more important of his works appears below. The date shown is that of first publication.