Originally known as the Liberal Action Group, Radical Action was a pressure group of rank and file members inside the Liberal Party during the Second World War, opposing the party truce which the leadership had entered into with the Labour Party and the Conservatives. Radical Action also sought to distance the party from the Liberal Nationals. Fothergill later maintained this stance, particularly in respect of the proposed Liberal-Liberal National merger talks which were progressing in Scotland during 1946–1947 the terms of which Fothergill, together with party leader Clement Davies and leader in the House of Lords, Herbert Samuel felt were totally unacceptable. Fothergill became a leading member of Radical Action, holding the position of Treasurer. Importantly, in view of Fothergill's later role in party organisation, Radical Action also wanted a radical overhaul of the party's electoral machine. Fothergill had become Chairman of the Liberal Party in 1946 and held the post until 1949. In this role he played a significant part in party reconstruction and under his leadership the re-establishment of many local and constituency parties took place. At the 1947 party assembly, Fothergill reported that over 500 active associations existed compared with only 200 some eight months before. This led to the party putting up more candidates the 1950 general election than they had since 1929. The strategy served the party well, even in the wake of the very poor results of the 1950 and 1951 elections, as the broad structure of the party on the ground was maintained – unlike the 1930s when many local associations just disappeared. Together with other committed party officers like Edward Martell and Frank Byers, Fothergill helped sustain the party through some of its darkest days. According to one commentator who knew him well, Fothergill was the closest the Liberal Party had to a Herbert Morrison, someone with an acute political brain who knew the value of organisation. From 1959–1952 Fothergill was President of the party; he was again chairman in 1952  and was Joint Treasurer from 1954–59. From 1954–1955 he served as president of the National League of Young Liberals. Fothergill also served as a member of the executive committee of the Scottish Liberal Party and as sometime Chairman of the Scottish Liberal Agricultural Committee. Jo Grimond later said of Fothergill that it was tragedy he never got into the House of Commons or that Life Peerages were not invented in his lifetime. Reflecting his radical, nonconformist background, Fothergill was a strong advocate of temperance reform and the evils of alcohol.