Mainwaring succeeded in winning a very narrow victory by 972 votes."The Times House of Commons, 1945", p. 106. He was a notably less frequent speaker in the post-war Parliaments, but kept up his allegiance to the left. In 1946 he broke with the whip to support an amendment to the Civil Aviation Bill which required the directors of the new airline corporations to be full-time, and to oppose a Lords amendment affecting the Air Traffic Advisory Council.Philip Norton, "Dissension in the House of Commons" (Macmillan, 1975), p. 10-13. However Mainwaring opposed an amendment to exclude men from Wales and Monmouthshire from the liability to do National Service, declaring that "no decent man or woman in Wales would support the amendment".Philip Norton, "Dissension in the House of Commons" (Macmillan, 1975), p. 23.
