The empire aside, concentrating on the United Kingdom itself, the roots of British democracy go back hundreds of years.
The British parliamentary system of government evolved from an autocratic monarchy into a constitutional monarchy and from a parliament with little real power to a democratic parliament.
The German system, on the other hand, continued to be an autocracy, ruled by an autocratic, archaic relic of a bygone era. This system continued in Germany until 1918, until forced to change by a world war.
Germany has long been a militaristic, aggressive nation, the main aggressors and the main cause of two world wars. Such a culture makes it difficult for democracy to take root and flourish.
WASPs.