In the UK, you should do that.
As far as I know, most people there do not know that you have to write a paper (and get it passed) in order to call yourself "doctor".
However, you CANNOT write "Dr. John Doe" on your card.
You have to write "John Doe, M.D.".
Therefore, in spoken language, you can call yourself "doctor" (or do you want to say "I have studied medicine in Germany where you have to write a paper to get your title, but I didn't do that until now and because of the different education systems, we have problems with differentiating those two ways of using the title" every time?), but you cannot write "Dr. John Doe" (but "John Doe, M.D." instead).