Why the Soviet Union appeared in British threat planning

Why did the Soviet Union appear on British inter-war threat lists?

Because Britain had recently opposed the Bolsheviks in the Russian Civil War and feared Soviet pressure toward India.

Britain had supported White Russian forces until roughly 1920, leaving a recent history of direct hostility with the new Soviet state. British planners also feared Soviet movement or pressure toward India. Those concerns made the Soviet Union relevant to imperial and naval planning even when another European war was not imminent. British threat lists ranged beyond Germany, Italy, and Japan.