This what if opens a lot of political possibilities that could be spun in a certain way. I'll explore some of them.

I think that Germany and the USSR would go by the dictum of "the enemy of my enemy is my friend." While the two face the UK as a common foe, the leaders of Germany and the USSR would most probably not choose to go against each other. Under this what if, Stalin may have miscalculated that Germany would get bog down in France. The USSR and the Germans, however, would be hard pressed to push their own campaigns because they would have to set aside sufficient forces to prevent a stab in the back.
Historically, Churchill distrusted Stalin so a USSR attack on British interests would reinforce this.

However, such a tentative alliance between Germany and the USSR would allow Germany to continue the trade of important materials. This would ease the historical supply problem of Germany and perhaps allow a more efficient German weapons development program.

Would this situation allow Germany the time to allocate enough resources to invade England? Perhaps. The important factor would be what the US would do. Most probably the US would support the UK and distract the US attention further away from the Pacific.

At this time, Japan has not yet opened hostilities with the UK and the US, so it's possible that some segments of the US govt might see the opportunity to use Japan as hedge against the Soviets. Historically, Japan and the USSR were rivals and the US, which is not yet an active participant in the war, might use this avenue. This might lead to the US turning a blind eye on China in exchange of assurances that Japan might help the UK against Russia. There is a factor that could temper this and that is the previous German-Japanese pact. Would Japan honor it if courted by the US?

Probably no. There are segments of the Japanese govt and military that prefer that the US not be antagonized. The USSR action against British interest would play right into their hands and could be a card to use with the US. Chiang's US support would evaporate in this situation. The Russians might increase support for Mao because he would be going against Japanese forces in China.

US support for Japan would obviate Japan's need to expand across the Pacific and allow Japan to concentrate against China while harassing the Russians.

Thus, with this what if, it's possible now for the US not to become an active participant in the war, especially with an active isolationist lobby. This scenario, of course, depends on Japan not going against British or US interest in Southeast Asia. US businessmen, I think, would grab at this chance to make money from supplying war material to the UK and its allies, plus maybe Japan. Combine the isolationists with business interests and that would be a powerful political force for an attempt by the US govt to actively participate in the war.

Of course, a non-belligerent US wouldn't prevent individuals or organizations from recruiting US volunteers to actively fight in the war.

As to the British in Palestine, they would be very hard put trying to defend from an attack on two fronts. Fortunately for the British, with Japan not expanding into Southeast Asia, the UK could free up more resources for use against a war with the USSR and Germany.

However, the Russians would face formidable natural obstacles, plus a mammoth logistical problem, in trying to grab the areas mentioned in this what if. The UK would also have an advantage here because since there is still a level of distrust between Hitler and Stalin, something that the historically canny British could exploit.