I have friends who have studied at IC and I have a post graduate degree (humanities) from UCL.
IC is very international and a cutting edge top science university. Your ds must be very good and hard working to have been offered a place, congratulations.
I have read the ft with huge interest.
Lodon is amazing, vibrant, cultural and all the rest of it but it is not for the faint hearted. Young students have to quickly learn to be self-reliant and yy to commuting longish distances on crowded tubes, it's expensive going out etc. etc.
All this is only worth it and doable if and only if you want to be at a cutting edge world class university and engage with people from all over the world. Those Chinese students some people seem to be dismissive of may turn out to be outstanding professional contacts in the future. I doubt that there is zero contact between foreign nationals and UK born students; sure people may gravitate to people who speak their own native language but there will be interactions in the tutor groups, prosily group work the student bar etc. etc.
What I'm trying to say is that if your dc is as hesitant asOP about the international aspect of IC he should give it a miss because he would be miserable. I believe for the right candidate, bright, talented, self reliant, resilient and open-minded who embraces the world out there IC will be outstanding.
Sadly I almost get the sense that OP wishes IC didn't have so many foreign students (which of course would make it less of a weld class institution). To me that shows a rather closed mind. In my opinion.