Knowing and studying Islam from its native Arabic grassroots, and living most of my life between all kinds of Muslims, I can tell you this: Muslims do not need to become a majority to take over a nation politically. The real benchmark is 10%.
Once they reach that threshold, they generate enough organized, consistent, and relentless pressure to begin reshaping a society from within. This is exactly what happened in the Middle East, Islam ruled for centuries before Muslims were even a majority of the population. They will do the same in Europe.
The Islamization of culture accelerates once political leverage is achieved; but achieving that leverage never required a majority. Islamic doctrine is extraordinarily well developed on this point; it has centuries of refined methodology for how a minority captures political power, then gradually Islamizes the culture until the demographic transformation becomes irreversible.
The British and Europeans have no idea what they are dealing with. They look down on Islam as a primitive religion; a relic, a curiosity. They do not see it for what it actually is: one of the most sophisticated and battle-tested systems of political conquest ever developed by human civilization.
By the time they realize it, 10% will be a distant memory.