"The Schengen area allows movement between member states without birder checks, the same way as we can move from London to Birmignham without passing through a visible border. That is a fact

Oh no it is not! The facts below. As I have alluded to many times before.

http://www.infomigrants.net/en/post/8750/border-controls-in-europe-s-schengen-zone

Also certain countries have random road blocks as a matter of course.
From firsthand experience the Guardia Civil in Spain and An Garda Síochána in Ireland frequently set up random road blocks. In Ireland this can include other government departments to check ID and possession of PPS number. There may be a theoretical freedom of movement, but the reality is that border checks have been introduced,justified by fears of terrorism, and random internal checks occur in certain countries to endure that those stopped have a right to be there. And to stop the little fellow that likes to dispute everything I say about Ireland a link is supplied below to confirm what I have said.

https://www.independent.ie/irish-news/garda-social-welfare-inspectors-and-revenue-officers-all-present-at-multioperation-road-ch