Records for the East India Company are comprehensive and easily researched however I notice you refer to "India Trading Company" so I wonder if the East India Company is what you are really looking for. It was so famous and so powerful that I heve never heard of it being referred to as anything but East India Company. You also mention that census returns say that the person you are trying to trace appears as a Store
Clerk in the India Office. The India Office was the government department which dealt with everything referring to India at the time of the British Raj, created in 1858 when the East India Company lost its powers. I wonder if your man was not simply a Civil
Servant working in the India Office in
London? It is possible that they still hold records of their employees. Might be worth a try.