For citation, I recommend a book by Garret Jones, “The Culture Transplant: How Migrants Make the Economies They Move To a Lot Like the Ones They Left”

https://www.amazon.com/Culture-Transplant-Migrants-Make-Econ...

It matters because the nature of a country reflects the culture of its population, and immigrants bring along the culture of the places they are from: https://www.amazon.com/Culture-Transplant-Migrants-Make-Econ....

The large influx of south Asians to the UK will make the UK different. And if you think the UK is a better place than India, those changes will probably not be great ones from your point of view.