The common knowledge among those interested in the history is that Britain insitutionalized and entrenched caste in an administrative framework that never before existed in India.

They generally saw their colonial subjects as tools for financial gain and wished they could stay out of the messy sociologic aspects of how different people may relate to each other. On a more fundamental level, they didn't see them as people.

They also implicated skin color in caste in a way that it was not previously. Their perception of the world at the time was very much "white = good" and "anything other than white = bad" and they couldn't help but apply that framework to all human relations.