Who built Britain's economic-war picture?

Was British economic-warfare planning handled by a commerce department, or did the Royal Navy do the work itself?

Relevant departments supplied information, but the Admiralty conducted much of the planning and sometimes trusted its own intelligence more than the civilian data it received.

Britain did not have a direct equivalent of the modern American commerce department described in the question. Civil departments held useful trade and resource information and passed it to naval planners. The Admiralty nevertheless built and checked its own picture of Japanese imports, stockpiles, and vulnerabilities. Naval intelligence could sometimes be better than the departmental returns, which made institutional cross-checking part of the blockade plan.