Using a combination of religious and secular knowledge I can say with a high level of certainty that within 50 years both Britain and Germany will be Muslim.
The Quran predicts that Islam will supersede all other religions (61:9). In (5:54) it says that if Muslims don’t follow Islam then God will replace them with another people who will.
There is a
Hadith that says that one day Muslims will be like the foam of a sea—vast in numbers but weak because of fear of death and love for this world. There are many Hadith that predict that Jesus will return.
For the first few hundred years Islam was led by Arabs. After the Mongol invasions, by around 1250, leadership of the Muslim world got transferred to Turks, which lasted till around 1918. Transfer of control from one people to another has happened before.
With the above information in mind, I think that Muslims of today have failed and there is another change in leadership due. The arrival of Jesus will be the critical point. People of European descent will become Muslims and assume the leadership of Islam for the next few centuries. The British and Germans will be an important component of that.