Tate was one of two members of the Vietnam Solidarity Campaign organising committee for the demonstration against the Vietnam war in London in October 1968 who successfully opposed a proposal to halt the march in Whitehall, which would have caused unnecessary confrontation with the police and a degeneration into violence. He was thus instrumental in ensuring that the 200,000 participants passed through London peacefully, despite dire prognostications in the press and on television (who reported the march but also gave undue coverage to a simultaneous 5,000-strong violent counter-protest by Maoists attacking the United States Embassy). As a result, opposition to the war grew enormously in Britain at the same time as in the United States. At the time of the demonstration, The Guardian described him as "an able Ulsterman in his early thirties, with unmodishly short dark hair, the black-rimmed spectacles of an advertising executive, and a terse, direct, manner".
