The London station, San Pancras looks really beautiful
I was from the local station in London San Pancras and my destination was Paris, Gare Du Nod. It was a 2 hour and 15 minutes ride from London, without any stop.
To be quite frank, Gare du Nod is a little scary place to be. A lot of people, beggars, and all the horrible reviews I read online seem to apply.