During the late 1950s and early 1960s MB became involved with several political causes. She joined the Campaign for Nuclear Disarmament (CND), and was arrested and roughed up by the police on a demonstration of a thousand people outside the airforce base at Ruislip. She sent a long letter to Nye Bevan and Jennie Lee on 8 July 1958 (later in the year CND was founded), asking them to clarify their position on nuclear disarmament. She was also elected to the general council of her union, the Association of Cine and Television Technicians , and she went as their delegate to the Women's Labour Party conference at Blackpool. She was, however, opposed to holding a separate women's conference, and believed that after forty years of suffrage women should feel free to speak while standing shoulder to shoulder with men. She also became a member of the Married Women's Association and the Six Point Group , which she later chaired. It is therefore a mistake to suppose that she did not belong to any explicitly feminist organisations or networks. She also made her feminist opinions plain in both her life and her writing. After her second marriage she became an increasingly active campaigner for women's rights, and an ally of Edith Summerskill in attempting divorce reform.

Not long afterwards, she and her friends in London were pursuing street politics to the left of the Labour Party , like mounting a carnival float at a CND festival to represent and caricature Real Women as glossily produced and sexily displayed to attract and to pleasure men. This was the carnivalesque and amusing side of feminism. The female house-mates launched a consciousness-raising group which still lacked a vocabulary for many of the subjects it wanted to discuss. (Sex was a harder topic than the fact that straight men didn't dream of doing housework because it was women's work; lowly work, a problem many revolutionary men refused to discuss.) After other women joined the group, a couple of husbands stalked in and yanked their wives away.