It is probably the most connected not-tiny island.

(One of the world's biggest airports, several of Europe's busiest, frequent direct rail connection to the continent, frequent ferries on many routes, fully integrated free trade + work zone.)

"According to Getlink, the company which operates the Channel Tunnel, 1.64 million trucks traveled between the UK and the EU using the crossing last year. More than 2.5 million cars made the crossing, as did 51,229 buses and 2,012 freight trains.

Added to the even greater volumes of truck crossings made on ferries — the Port of Dover handled a record 2.6 million trucks in 2017, according to its own figures — it accounts for a massive annual volume."

The UK could have closed all these borders down. They just chose not too.

The UK could not close those borders down, we would starve.

... you can still unload freight. You limit the movement of people though.

People love to make excuses or put up obstructions to an idea, but solutions are almost always achievable with a little planning, resources and the will to make it happen.

Not to mention it has double the population of Australia and 80x the population density.