If you compare the Brits' handling of large-scale immigration with the similar Oz experience over decades, you'ld have to say the Brits don't come out of it very well.
Oz is currently feeling some discomfiture with post-Covid immigration levels over 500,000 annually. But there is widespread recognition that many of the migrants are energetic young people with skills the Oz economy sorely needs.
My experience over 40 years living in Oz was what a wonderfully rich (in all senses) country immigration had made of Oz, and sensible people on all sides of politics recognized this. I had many young staff working for me who had different coloured skins and unpronounceable surnames, but when they opened their mouths they spoke broad Australian. They were fine young citizens.
Of course British circumstances - population & geography - are different from the Oz reality. But clearer recognition of the positive contribution immigrants make would be helpful.