I havr only skim-read, so apologies if I repeat...but why are you 'shocked'? London is a huge, global city - a centre for immigration for reasons of business and commerce, as well as the 'immigration' people associate with refugees and asylum seekers.
There are many, many people here who a escaping war and genocide. There are also economic immgrants from the EU....and Aussies/Kiwis/South Africans bumming aroud doing bar work for a few years...and Indian doctors and Filipino nurses filling skills gaps...and Russian oligarchs / Saudi princes etc using London as a playground....oh, and many many hundreds of thousands of black British, Aasian-british, mixd race etc people who are BRITISH, just not white...etc etc
Is it just the non-white, visible and possibly poor 'non white Brits' you are worried about?
Whatever your issues....I dont understand why you are shocked, unless perhaps you are not from London or havent been here lately!