I'm not sure about the population density in the entirety of London, but I do know my student accommodation was in a largely Islamic area.

I'll never forget the three young men in suits who sheepishly sidled up to me one evening when I was on my way home from uni, mumbled something so shyly and quietly that I couldn't make out a word, handed me a leaflet and quickly walked off. They still rank as one of the nicest "religious people" encounters I've ever had.

Oh, and every day I had to walk through not insignificant crowds on one particular street (I think there must have been some kind of prayer area nearby Actually there are several mosques fairly close, so they must have all been coming back from there since they'd all be gone if I got up an extra half hour late) and they never once tried to blow me up either! Even though sometimes I did used to stare at them in their whiter than white clothing, I still don't know how they got them so pristine, I wish I could get my whites looking so fantastic. :(