The special effects for the film look great. I particularly like the part where a Tube zooms past and the children see the technicolour world of Narnia coming out from the windows inside.
You can see the "Teaser Trailer" in full below from official site's global widget. It's in the "videos" section from the menu:
The outside shots look like they're trying to re-create the Strand at Charing Cross and it would be with ironic if the inside was filmed at the Strand at Aldwych. A number of movies are shot at the now closed Aldwych, when a Tube station needs to be created, but with a Walt Disney budget, I'd imagine that an entirely new set was built.
Hopefully a Leslie Green or retro London Underground station architecture expert will be able to prove me wrong or right!