The loss of Singapore was the worst defeat in British history, with hundreds of thousands of troops entering captivity and many dying. The full scope of the Allied POW treatment at the hands of the Japanese was not fully known until after the war.
The immediate effect of the Japanese attack was to bring America into the war. As set out in the Atlantic Charter of 1941, Churchill and Roosevelt wanted to deal with Hitler first and then the Japanese. Circumstances in the Pacific prevented most of the American forces from being deployed to Europe until late 1943.
After the defeat of the German Navy, the British sent a sizable force to join the Americans in the Pacific. Task Force 57 had four fleet carriers with armored decks, which required less maintenance after bomb or kamikaze hits than the Americans, whose carriers had wooden decks.
Britain, like the United States, mobilized very early on for total war production. The home front considered Hitler the primary enemy, but nevertheless supported the expected invasion of the Japanese Home Islands.
England was financially and physically devastated by the war, and sent only a token force to occupy Japan.