The British government planned to imprison Sam Wanamaker, father of British actor Zoë Wanamaker, in the event of an emergency in relations with the Soviet Union in the 1950s.

Secret MI5 files released today show that the secret services intended to imprison Wanamaker in an internment camp "in the event of an emergency with Russia", because of his communist sympathies. The Chicago-born theatre director and actor went on to raise millions of pounds to rebuild Shakespeare's Globe theatre in London and is now commemorated with a blue plaque beside the building as a visionary.

According to the files, MI5 was particularly concerned about Wanamaker's work with the New Shakespeare Theatre Club, based in Liverpool, where he was artistic director. Surveillance included intercepting letters and eavesdropping on conversations with members of his circle. Secret service officers concluded the theatre group was "intended to be used as a vehicle for disseminating extreme leftwing propaganda under the guise of culture … and, if successful, will be a great asset to the Communist party". MI5 was concerned that it staged plays such as Tea and Sympathy, written by Robert Anderson in the wake of the hysteria associated with McCarthyism in America.

Wanamaker moved to Britain after he was blacklisted by the House Un-American Activities Committee for his growing interest in the ideals of communism. Once in Britain he was careful to keep his political activities muted. A letter dated 22 May 1952 intercepted by MI5 revealed Wanamaker telling Pamela Knelman, a Canadian who was organising a London gathering of communists in the film world, that he must "tread with careful precision on matters involving peace which has now become a highly political and controversial subject". Nevertheless, MI5 stated Wanamaker was "recommended for internment in the event of an emergency" because he was "known to have maintained his communist sympathies and contacts".