Much exaggeration. The UK is around 5% Muslim, London is perhaps 10%.
The article is talking about a single neighborhood. If 90% of that 10% figure you posted live in one area, it would be overwhelmingly Muslim, just like the article describes.
But as London goes, so goes England, and as England goes, so goes the UK—a large body reaching critical mass has a great impact. London may only be 10%, but I bet the percentage under the age of 10 is much, much higher. And I bet that culturally the non-Muslims are much more fragmented.
Just wait until they spread from Rotterdam Holland. Some cancers spread slowly, but spread they will.