The Eurostar trains leave from London St. Pancras Station, in a secure area. It was advised that passengers arrive at least a half hour before train time. We went through an airport type security check, and passport control, before entering this boarding lounge area. I was legally in France, my passport was stamped "Londres" (French for London).
Ready to board. The train to Paris also boarded at the same time.
Speeding through Kent County, southeast of London. The Channel Tunnel Rail Link between London and the Tunnel is a completely new railway, and a separate operation from Network Rail which operates the traditional British Railways infrastructure. This line uses cab signals, unlike Network Rail which still uses the old British Railways intermittent inductive Automatic Warning System. And higher speeds are thus possible on the Channel Tunnel Rail Link.
Speeding through France now. I timed the passage through the Channel Tunnel at 22 minutes. Speed through the tunnel is limited to 160 kmph, or 99 mph. I was legally in France but never set foot there. The train made an intermediate stop at Lille.
The train speed was occasionally displayed here, a little below the 300 kmph speed limit. Still, 295 kmph is about 183 mph.
After arrival at Brussels South Station. With the Schengen Agreement established in 1995, most countries in Continental Europe have eliminated customs checks at the border crossings. Because I was legally admitted to France, I was legal in Belgium too. So I was clear to exit the platform, exit the station, and walk to the hotel.