Your passport should be valid for the proposed duration of your stay; you don’t need any additional period of validity on your passport beyond this.
The German authorities have confirmed they will accept British passports extended by 12 months by British Embassies and Consulates under additional measures put in place in mid-2014.
UK Emergency Travel Documents
UK Emergency Travel Documents are accepted for entry, airside transit and exit from Germany.
British Citizens don’t need a visa to enter Germany. If you hold a different type of British nationality, check entry requirements with the German Embassy.
Stays of longer than three months
If you intend to work or study in Germany you must register with the German authorities (Einwohnermeldeamt) within 3 months of arrival. There is no longer a requirement for EU citizens to apply for a residence permit.