Zeee Germans

While some take it seriously a lot of British lightheartedly still associate Germany with impending doom due to WWII. For example my English friend started doing weights in the gym and his brother facetiously said 'you getting ready for the Germans?'. In this case he's mocking the German accent as well. It's just a joke.

Yours sincerely, General Joseph Liebgott

Also it refers back to war comics that were popular with a previous generation.
The speech of german soldiers was along the lines of "vot iz your name", "you vil anser ze questions englander"