The change you saw is mystifying to me, as the only mass migration to the UK since 2000 has been white Eastern European. The non white groups that make up ethnic Britain have been here since 1948, Muslims since the early to mid 50’s.
As to Manchester, that DOES have a reputation (in some areas) for crime, but that crime is drug based: white and black gangs, not Muslims.
I’m sure the Rotherham scandal was a shock & mystified many
btw - according to the census... between 2001 and 2011, the general population of England alone, increased by a little over 4 million people. Of that 4 million, over 1 million identified as muslim. And the number of mosques more than doubled in that 10yr period, from 600 to 1500