Why Britain avoided a larger Bolshevik breakthrough

Would the cost of a postwar naval race have pushed Britain toward Bolshevik unrest?

No. Revolutionary communism remained limited because Labour and other strong center parties absorbed much of the political pressure.

Interwar industrial and union conflict did not amount to a genuine Bolshevik takeover threat. Britain still faced serious unrest, but it retained unifying institutions and a strong Labour Party that represented working-class politics inside the parliamentary system. Durable center-left and center-right parties denied extremist movements much of the political space they needed to become mainstream. The 1920s Labour Party was not communist. Naval spending therefore did not automatically imply state collapse.