It’s pretty plain on DHH’s blog: 

In 2000, more than sixty percent of the city were native Brits. By 2024, that had dropped to about a third. A statistic as evident as day when you walk the streets of London now.

I wonder what characteristic he uses to define « native brits » that can be seen when walking.

Or just take a look at his twitter. Which Framework obviously did since they retweet a lot of his posts…