Unfortunately I don't have the time to write a longer and fuller answer, but I will reference a previous related answer on British anticolonialism I wrote here which outlines the ideological underpinnings of anti imperialism in the CPGB.

In Britain at least, it's difficult to pin down a coherent response owing to changing circumstances and, more importantly, the different opinions of various individuals who made up the Communist Party of Great Britain. Generally, communists supported immediate and full decolonisation on the understanding that decolonised polities would undergo proletarian revolution owing to their struggle against the imperialist system which, as u/RevMLM notes, was seen as inexorably and inseparably linked to the capitalist system oppressing the proletariat in Britain. Decolonisation was a means of, or even a necessary step in weakening imperialism and hence bolstered the chance of revolution "at home." Once the British Empire had been dismantled, Britain would undergo revolution and then unite in brotherly commonality with former colonies as an equal partner as they strove toward communism.

To answer what would have happened if they came to power I think is a very difficult question to ask and risks drifting into counterfactual. I have found nothing in the CPGB archives amounting to a coherent and workable policy for the colonies in the event of seizing power aside from commitments to ensure full and complete national liberation. The reality is that if any colonial power was to undergo a communist revolution, any colonial policy one way or the other would likely be a moot point as the imperial state would have been dismantled from the centre and it is very difficult to see how any communist party would be able to exert control in the former imperial colonies one way or the other.