You might want to check out Susan Pennybacker’s From Scottsboro to Munich–though it focuses on a slightly later period.

Good question! In the early Comintern, the British CP was prominent in discussions of the colonial question. At the Fourth Congress, British delegates spoke strongly on the obligations of “metropolitan” parties toward colonial subjects, and a British delegate joined in a statement of protest that the congress was not paying enough attention to this issue. However, the topic you pose is vast. It’s important to study this not only from the point of view of the British communists but from that of the communist groups in formation in the colonies, especially India. One Indian scholar has written — with an eye to the Stalin period — that the “colonial” parties fared better when they were spared the attentions of their comrades in the colonizing power.