What are the laws of Germany? I think that would be the determining factor and England wouldn't have a case, unless your character signed some kind of confidentiality agreement. If an agreement was signed, then the breach would have occurred in England even though the action took place in Germany. If it's just based on the law and no agreement, then I would believe the character is safe.
However, after writing that I'm starting to doubt myself. I remember hearing about some United States federal agents traveling to a country where prostitution is legal and got some hookers. Since prostitution is still a federal offense in the US, and they were citizens of the US and conducting official business, I believe they lost their jobs and were reprimanded.
Not sure if that would apply to just a citizen. Though I tend to remember hearing something that if a US citizen travelled to a country and had sexual relations with a minor, he or she would be prosecuted upon return home under US federal law. If that's the case, then that would refute everything I said above.
Again, I didn't research anything nor do I have any legal background. Just trying to logic through it. Good luck on writing your character for your book.
