I have always felt that getting rid of the License Raja under the British would have helped. It is my understanding that the Indian Socialist used this office as a way to control business. With less government approvals required, the Indian business sector would have grown and lead to a more prosperous India. Also change the regulations so that contract bids for work with the Indian railroads and other government projects could be submitted in the capital of India versus London during colonial times.
Finally encourage British business to open factories and offices in India. Besides strengthening the business sector, it would tie the Indian economy more to the British economy. As India grow wealthier, then Great Britain would benefit from their investments in India.