3c. Will I lose my German citizenship if I acquire British citizenship?
Under the German Nationality Act (in force since 28 August 2007), a German does not lose his/ her German citizenship if he/ she acquires citizenship of another EU member state or of Switzerland. The United Kingdom has not been a member of the EU since 31 January 2020, and the transition period ended on 31 December 2020.
Under Section 3 (2) of the Transitional Brexit Act passed by the German parliament on 17 January 2019, Germans who have made an application for naturalisation in the United Kingdom before the end of the transition period (31 December 2020) do not lose their German citizenship pursuant to Section 25 (1), first sentence, of the Nationality Act, even if the citizenship ceremony marking the acquisition of British citizenship only takes place after the end of the transition period.
This means that, if you were naturalised by the British authorities or applied for naturalisation before the end of the transition period following Britain’s withdrawal from the EU, you will not lose your German citizenship, and neither will you need permission to retain German nationality. It is the date of the application that counts here, not the date of naturalisation (citizenship ceremony). It is essential to retain proof of the date of your application (see question 3d).
However, if after 1 January 2021 you apply for and acquire British citizenship without having previously received permission from the Federal Office of Administration to retain German nationality, you will automatically lose your German nationality. You can find detailed information on Retention of German citizenship upon naturalisation in another country here.