I am sorry to disagree with this assumption: from 1874 on, a civil marriage necessarily precedes any religious marriage in Germany (and then Prussia) – until now.
Berlin was a melting pot with various religious communities and If you wanted to 'be different' you could. In a smaller town, people would have cared but not in Berlin. There must have been a different reason. My guess is missing documents and fewer questions in London...
Regards from Germany
Corinna (Wöhrl), Hoisdorf