Hirohito as a political prize in a divided Japan

If an invasion divided Japan like Germany, would Britain support keeping Emperor Hirohito?

Probably; preserving the throne could provide a symbol for eventual reunification and deny the Soviets an important source of political legitimacy.

Britain would likely favor eventual reunification if Japan were divided into occupation zones. Retaining Hirohito could provide a common institution around which the non-Soviet zones claimed national continuity. That would make control of the emperor a political contest among the occupying powers rather than only a legal question about prosecution. Surrendering to the British or Americans would be far safer for Hirohito than falling into Soviet hands.