When the cops stop you on the street and ask for your digital ID and you can't show it to them, they'll take you to a deportation center. #PapersPlease
"Tourism in the United Kingdom is a major industry and contributor to the U.K. economy, which is the world's 10th biggest tourist destination, with over 40.1 million visiting in 2019, contributing a total of £234 billion to the GDP"
Like the US, I think there are multiple interest groups, not all of whom are interested in seeing "aliens" on British streets. I was named a "Highly Skilled Migrant" by Her Majesty's Government of the United Kingdom and Northern Ireland and paid a fair amount of money to the University of Liverpool and yet, never got the feeling I was in any way anything other than a foreigner.
The same way other things "help" migration. By making life very difficult for you if you aren't a proper citizen. I imagine the outcome for this would be to make it nearly impossible to do anything with the government or doing anything you might need an ID for, especially online. Some citizens will probably suffer too, but it is a price the government is willing to pay.