A countdown clock is illuminated at 10 Downing Street on Brexit day in London, Britain January 31, 2020. REUTERS/Toby Melville

LONDON (Reuters) - The United Kingdom finally cast off from the European Union on Friday for an uncertain Brexit future, turning its back on post-World War Two attempts to unite the once warring nations of Europe into a global power.

In its biggest geopolitical shift since the loss of its sprawling empire, the United Kingdom slipped away at 2300 GMT - ending 47 years of membership in a step cast by Prime Minister Boris Johnson as the dawn of new era.