Reference your telegram 162. 
Circular Z.66  was despatched subsequent to discussions with the Foreign Office at which I had urged the importance of a joint declaration and drawing up some line beyond which Japan should not go. Foreign Office rapprochement is necessary in the first place to determine the limits of our vital interests before approaching the United States. This is, I think, reasonable. Have submitted that this is a matter for the Chiefs of Staff You will recall that Dominions Office telegram 180  stated that the step which should constitute an act of war by Japan could only be decided by the Governments in the light of circumstances at the time.
I have included this item in comprehensive memorandum on the Far East strategy  already submitted for examination by the Chiefs of Staff and discussion by the Defence Committee, which Churchill has agreed to convene specially for this purpose.
Will advise you further.