Schengen doesn’t require visas, but they still have border checkpoints, don’t they?? Last time I visited Europe I visited the UK but didn’t go anywhere else in the EU. Jeez louise, they gotta at least have checkpoints.
I haven’t traveled in Europe for almost 20 years. But when I went across borders on a train back then the conductor came through and I had to self-identify as an American, show my passport and explain where I was going and what I was doing. Other people, presumably locals, did nothing.
There are no checkpoints. There can be a random check, but the only time I have seen it was when driving from Netherlands to Germany. That was probably because weed is legal in Netherlands and not in Germany. Probably also during the big soccer games as some notorious hooligans have temporary entry bans during these.
If you are in a Schengen country and go to another Schengen country no border controls. UK is not a Schengen country.