UK is not a Schengen country...so not sure where you got that info. You have to go thru UK customs when going from EU country to the UK
Reality is people are realizing that Open Borders and Free Trade do not work....and the Brits are figuring out that there is only so much Socialism that can fix the mess caused by the EU and its failed Free Trade and soverignity robbing programs.
Sorry, what I was referring to was the ease of travel, no visas needed, UK citizens travel under an eu passport, passing through customs only is a slight inconvenience, and if you’re a UK passports holder, a formality.