You can hardly claim that after 1929 Britain ‘leapt leftwards’. The 30s were dominated by cross-party government that segued into wartime government in the 40s. Then came a 50s post-war consensus around the mixed economy. The only break with this cross-party tradition is the present homeownerist consensus around the need to keep house prices ahead of inflation, not because any party dissents, but because it is so unusually divisive. One of the last things Labour did in 1931 before it was swallowed by coalition government was to institute a land value tax that would have prevented this.