Regarding the demographics of London, I borrow from Rod Liddle writing about why there was such a large 'remain' vote in the capital, but it applies also to this topic.
" The inner London boroughs voted heavily for remain not because of enlightened white British folk who welcome diversity, but because the overwhelming majority of people in these boroughs are immigrants or the offspring of immigrants themselves. Newham, Tower Hamlets, Lewisham, Southwark, Hounslow, Lambeth. Waltham Forest, Brent, Islington, Camden and many more, all have a white population which is now below 50%. In Newham, the figure is staggeringly just 16.7 %, in Brent 18%. The white British have moved out long ago to the ring around London - which is why Sutton, Bexley, Barking and Dagenham, Hillingdon and Havering all voted 'Out'. "
This I believe too, is a contributory factor as to why London now has a Muslim mayor.