I made an online requiry and it seems that you need a special approval from the German public authority responsible for aliens (in German: Ausländerbehörde).
A few internet sources gave the same answer to your question as this one:
(English translation by Google Translate)
Let me quote the important part:
"If a person entitled to asylum with permanent resident such as the purpose of studies seeking entry to the UK, so it is this is usually no problem, since he has a secure residence status. For him this but maintained he should be able to approve the more than six months ending abroad by the immigration office. After all, who is leaving for more than six months in Germany, loses permanent resident status, unless that is clearly evident that the stay abroad purely temporary nature was".