The correct option is Dependency on British industrialisation.

Step-by-Step Explanation:

1. Understanding the Impact of British Rule:
During the colonial period, the British government reshaped the Indian economic structure to serve its own industrial interests. Instead of fostering independent domestic industries, British policies systematically dismantled traditional Indian manufacturing (such as the famous handloom and handicraft sectors) through a process often referred to as de-industrialization.

2. Creation of Economic Dependency:
India was converted into a primary supplier of raw materials (like cotton, indigo, and jute) for British factories and a captive market for finished, machine-made British goods. This created a structural dependency where the Indian economy could not function or modernize independently; its economic cycles, trade patterns, and production were entirely subordinated to the industrial needs of Great Britain.

3. Why Other Options are Incorrect:
- Modernisation of thought and Sanskritisation of lower castes are primarily cultural or social dynamics rather than direct structural economic changes.
- Westernisation of mass media is a cultural and technological influence rather than a core structural change of the entire Indian economy.