Scott was a member of the Central Committee elected at the Eleventh Party Congress in December 1929. He had become a significant figure in the five-year old National Minority Movement, which campaigned for a united left front within the trades unions as an effective way of resisting attacks on working-class living standards.
The task was not to organise independent revolutionary trade unions or to split revolutionary elements away from existing organisations affiliated to the TUC, but to convert the revolutionary minority within each industry into a revolutionary majority. The NMM had seemed set to almost achieve this self-imposed task but the disillusionment following the general strike and a wider employer offensive on the back of depression created a difficult period.
Joe Scott was part of a trend in the engineering minority movement that discerned a beginning of a willingness to fight back emerging from depression. His pamphlet, “Engineers' Hours & Wages" was published in 1931 by the Engineering section of the Minority Movement. This pamphlet caused a sensation in the organised factories, but the Party now also took the view that the MM had become sectarian and insulated from the masses.
The Central Committee emphasised the need for a complete change in the policy of the Minority Movement, which is saw as a “small, self-absorbed organisation of leaders who have nothing to do with the real struggle of the workers”. Instead of going working among working people, the MM simply invited them “to take part in a highly `elaborate’ organisational structure”! The Party rejected abolition of the Minority Movement but called for the development of “a really broad trade union opposition in the reformist trade unions and in the factories”. [“The Communist International”March 15th 1932, pp 155-157], Vol. IX, No. 4/5,
Joe now became National Secretary of the whole Minority Movement, which was of course, essentially a creature of the Communist Party. But it set out for a new course under his leadership, with the assistance of Pollitt and Horner in particular. Contrary to those who emphasise the seeming negativity of the lines adopted in the so-called "third period", in far retrospective it seems that a new sense of reality had penetrated the higher echelons of the Party. An approach which has been called "constitutional militancy" surged the Party forward. Although far more well-known names were behind this, it was Joe Scott who had the daily responsibility for actually implementing the new way of approaching left unity within the unions. At times it seemed less constitutional and overwhelmingly militant. Wave after wave of unofficial movements, often in non-unionised factories, usually faced with issues that the official unions were agnostic over, saw tens of thousands of workers in west London and west Midlands pour into the official unions, changing them in the process, even if this did not become apparent for some years.
Following these experiences, in 1932, the National Minority Movement published "Strike strategy and tactics: the lessons of the industrial struggles", a textual embodiment of a new approach. Subsequently, in a direct reflection of this change in tone, Joe Scott became an elected member of the Amalgamated Engineering Union Executive Council, his union, representing the West Middlesex area, where the Communist Party had become highly influential in the developing new industries and now dominated the district.
Joe Scott was an assiduous mass campaigner for the Party, and would travel anywhere to speak, for example storming Maidstone in the early and difficult stages of the Second World War for a “Communist Crusade” meeting with Tom Mann.
He finally lost his North London AEU Executive seat in 1957 by just one vote to anti-Communist, T Chapman. Scott then retired from front rank trades unionism. But revenge for the defeat was secured by Reg Birch, then a Party member, who won an overwhelming victory three years later in the election held in February 1960 and announced in May.