Jacques joined the Communist Party of Great Britain at eighteen, and at both Manchester and Cambridge universities was very active in student politics. In 1966 he was one of the prime movers behind the Radical Student Alliance, a left-of-centre cross-party organisation of around 400 students from 108 universities and colleges which sought to build a students' movement 'able to take collective action on matters of general social concern'. At Cambridge he was instrumental in the formation of the Cambridge University Students’ Union. By 1967 he was a member of the Communist Party's Executive Committee, "probably the youngest member ever at about twenty-two", and he remained a member until 1991. Profoundly affected by the Soviet invasion of Czechoslovakia and the May events in Paris in 1968, which he described as his ‘political birth’, he was one of the early leaders of the Eurocommunist or reformist wing of the party, particularly influenced by the work of Antonio Gramsci. In 1976, in a report to the Executive Committee of the Communist Party, he argued that 'class struggle is not confined to economic struggle ... but is also ideological and cultural'. Later the same year he was chosen, with the traditionalist George Matthews, to finalise an updated version of "The British Road to Socialism" (the Communist Party's programme) to present to the Party's 35th National Congress in 1977. He later described the process as a 'Mexican stand-off', but the influence of Gramscian ideas was evident in the final draft, which called for a 'broad democratic alliance' and asserted that the progressive movement needed 'not only ... to be an association of class forces ... but of other important forces in society which emerge from areas of oppression not always directly connected with the relations of production'.