The posts regarding the viability of the Singapore Strategy when it was make good points, however, as the 1930s gave way to the 1940s the British should have started making some changes:
1. In 1938 when it was clear the Germans were getting aggressive and the Japanese were already aggressive, they should have started thinking hard about alternatives.
2. In 1939 after the war in Europe started they should have thought harder about alternatives.
3. In 1940 after France fell they should have started some serious worst case scenario planning.
4. In 1940 after the Japanese occupied FIC, they should have started implementing some worst case scenario plans because now all of the factors that made the Singapore Strategy a sound strategy are gone.
In Churchill's memoirs:
4th October, 1940 - Churchill invites Roosevelt to send an American squadron '...the bigger the better, to pay a friendly visit to Singapore...' ('Mr. Eden's Mission',
The Second World War, Volume 2)
8th December, 1940 - Churchill writes to Roosevelt that he hears the Japanese are '...preparing five good divisions for possible use as an overseas expeditionary force. We have to-day no forces in the Far East capable of dealing with this situation should it develop...' ('Lend-Lease',
The Second World War, Volume 2)
7th January, 1941 - Churchill wrote to General Ismay that '...If Japan goes to war with us there is not the slightest chance of holding Hong Kong or relieving it. It is most unwise to increase the loss we shall suffer there...' but Churchill notes that '... Later on it will be seen that I allowed myself to be drawn from this position...' ('The Japanese Envoy',
The Second World War, Volume 3)
15th February, 1941 - Churchill wrote to Roosevelt '...Many drifting straws seem to indicate Japanese intention to make war on us or do something that would force us to make war on them in the next few weeks or months... ...the weight of the Japanese Navy, if thrown against us, would confront us with situations beyond the scope of our naval resources... Everything that you can do to inspire the Japanese with the fear of a double war may avert the danger...' ('The Japanese Envoy',
The Second World War, Volume 3)
20th February, 1941 - Churchill wrote to Roosevelt '...I have better news about Japan... ...If Japanese attack which seemed imminent is now postponed, this is largely due to fear of the United States. The more these fears can be played upon the better...' ('The Japanese Envoy',
The Second World War, Volume 3)
24th February, 1941 - A record of a meeting between Churchill and the Japanese Ambassador notes that: '...The Ambassador said that Japan had no intention for attacking us or the United States, and had no desire to become involved in a war with either Power. They would not attempt to attack Singapore or Australia, and he repeated several times that they would not attempt to gain a footing or make encroachments in the Dutch East Indies. The only complaint which Japan had, he said, was our attitude to China...' ('The Japanese Envoy',
The Second World War, Volume 3)
4th March, 1941 - Churchill noted in a minute, after another meeting with the Japanese Ambassador that '...I do not think Japan is likely to attack us unless and until she is sure we are going to be defeated...' ('The Japanese Envoy',
The Second World War, Volume 3)
28th May, 1941 - Churchill, as an aside regarding the consequences of the sinking of the
Bismarck and the pressure that that took of the Royal Navy noted to Roosevelt that '...The effect upon the Japanese will be highly beneficial. I expect they are doing all their sums again...' ('The Fate of the "Bismarck"',
The Second World War, Volume 3)
20 October, 1941 - Churchill indicated in a long letter to Roosevelt about several matters '...I have not referred to the Japanese menace, which has seemed to grow so much sharper in the last few days, nor to the splendid help which you are giving us in the Atlantic, because we discussed these great matters so fully at our meeting, and events are telling their own tale in accordance with our anticipations. I still think however that the stronger the action of the United States towards Japan the greater the chance of preserving peace...' ('The Path Ahead',
The Second World War, Volume 3)
5 November, 1941 - Churchill indicated to Roosevelt that '...No independent action by ourselves will deter Japan, because we are so much tied up elsewhere. But of course we will stand with you and do our utmost to back you in whatever course you choose. I think myself that Japan is more likely to drift into war than to plunge in. Please let me know what you think...' ('Japan',
The Second World War, Volume 3)
There's a lot more (and a limit to how much copy-typing of quotes I can do in one sitting!), but I get the impression that up until February of 1941, Churchill
was seriously worried about Japan, then he seemed to believe that the United States had managed to contain the situation, and that at least until October, 1941, his policy was relying upon the United States to keep Japan quiet.
(edited to correct a couple of typing errors)