Most refugees constituting what is perceived as a crisis today are in fact from Syria. I'm sure there are others, but they are few relative to Syria. The cause, of course, being the Syrian Civil war.

Going by your example of 10K in London. London has a population of approximately 8.5 million and 10K of that is one tenth of one percent of the population of the city as a whole. Unless all Syrian expats go to London for months on end, it won't make a huge dent in the demographics.

According to an article appearing in a 2015 issue of the Guardian, London's population increased by 900K or 12% since 2001. That means London was naturally growing by about .85% per year. So at the end of the day 10K is about 1/8th of the annual average population growth in London. Granted some of these people may be in need of immediate assistance, but long term is more important as the short term won't break the bank.

You are correct regarding the notion of culture; however, bigotry isn't limited to racism.