What is the greatest mistake in British history?
While many Americans probably think that upsetting the colonists with "taxation without representation" was a huge mistake, it's impossible to think that England could have kept all the colonies to this day. The US would be like Canada is to the Commonwealth.
The only colony in the New World that remains a part of the country that owned it is French Guiana, which interestingly is makes it the only EU member in the Americas (and the biggest member outside of Europe).
As for appeasing Hitler, that was a colossal mistake that cost many lives. Chamberlain waving the Munich Agreement to ecstatic Londoners showed how clueess they were to the dark clouds gathering over Germany. Had they taken a harder stance against Germany they might have prevented the blitzkrieg and perhaps setup a better line of defense in France rather than having to fight for their lives over their own skies and endure night upon night of bombing because of France's capitulation.
So, what do you think Britain's biggest mistake was?