He joined the Union Movement on its foundation in 1948 and became a leading figure in the new party as both general secretary and the editor of the UM newspaper Union. Playing a leading role in the development of the ideology of the UM, Thomson initially supported Europe a Nation enthusiastically, but soon tired of the esoteric policy and in 1950 organised a brief and even more unsuccessful return to prewar policy.Macklin, Very Deeply Dyed in Black, pp. 54–5 He then came to advocate a "left-wing fascist" approach and argued that the UM should target the working class for support with anticapitalist rhetoric.Macklin, Very Deeply Dyed in Black, p. 63
