A few possibilities to consider.
If the USA entered the war in March (1941?), would this impact the Wally/Soviet alliance? Is it possible that with full US participation this early the Churchill government would be less motivated to nurture the Soviet alliance or provide material assistance? If the Wallies believed they were able to win the war against Germany without Soviet assistance, would the grand alliance survive even until the end of the war? If the USSR and Wallies were simply co-belligerents fighting the same enemy and not true allies, could this increase the potential for violent conflict between the two as the war drew to a close.
Left to its own devices, Japan would either conclude its war with China sucessfully or still be engaged in a major land war on the Asian continent. I am presuming "no pacific theatre" means the Japanese have not invaded western colonies and forced the US and UK to respond, so Indochina, Indonesia, Singapore, the Phillipines, etc are not in Japanese hands. Possibly the European war will end with Japan ruling a largely subjugated China and in a very powerful position, militarily and diplomatically. They would be the dominant naval power in the western pacific and a major Asian land power. They would be in a position to threaten both the USSR and Wally interests in the pacific, and probably in a hostile relationship with both. If a hot or cold war develops between the Wallies and USSR, Japan could seek to gain further influence or advantage by aligning itself with one or the other. For their part, I could see the Wallies seeking alliance with Japan to provide and "eastern" front to threaten the USSR, much as china served that role in the late 1970's