Japanese intelligence services and the British Empire.
The various colonial police services, and the British Intelligence services, had a very good idea about the extent of the Japanese Intelligence agencies penetration, of the fabric of various colonial nations. Despite the commonly healed belief, they were not a bunch of upper class idiots, spending their lives drunk and playing polo. While it was virtually impossible to infiltrate the Japanese networks, there was a good idea of who was in the game. However pressure from London, to avoid upsetting the Japanese, meant that no major efforts could be made to prevent the Japanese services from working. There were plans in existence to round up and intern all Japanese in the various colonies, in the event of war.
Now in the same way that the British had major difficulties in penetrating the Japanese networks. The Japanese had the problem that once war broke out, their own networks, would rapidly become ineffective. They had to try to find willing agents among the indigenous peoples, who were in positions to be able to provide worthwhile intelligence, and had a timely method of passing the information on. The intelligence war in the Far East, Pacific, was more based once war broke out, on signals interception, photo reconnaissance, and physical reconnaissance, with by mostly the Americans and British, agent running. Japanese treatment of indigenous peoples, and the loyalty of some minority groups, allowed them to run low level groups. The major problem was always communications, as with no neutral countries, radio was the only way to send information back.
The fact that the British are allowing various oriental gentleman to observe there recent training exercises, in an attempt to convince them not to become involved in conflict with them. This is a double edged sword, in that it both sends a message, and allows various agencies to watch them, watching us, watching them. I would expect that once war breaks out, the majority of the the low level Japanese agents will quickly be rounded up, most colonial administrations had plans in place to do this. If Singapore doesn't fall, and the British can maintain the FEIB in place, thus avoiding the disruption that took place IOTL, Britain is going to have a much better insight into Japanese actions than it did. And the Japanese will find that their insight into British actions, much reduced. The major problem for the British will still however be the same as it was, the lack of interpreters, and other than borrowing them from the Americans, it is going to take time to make good this deficit.
The Japanese will lack the access to British papers, and personal, and the numerous indigenous peoples who having seen the British failure, are inclined to turn coat. I can see major problems ahead of the Japanese as they are increasingly cut off from decent intelligence.
RR.