The 44% figure comes from the Greater London Authority, but should be clarified a bit. There is a BBC article[0] about this which states "... 44% of the city's people are now of black or ethnic minority origins".
I don't know if London demographics are the point of comparison, e.g. if you looked at FAANG's demographics you would not compare them to the Bay Area as their hiring pool is much wider than people who grew up locally.