One of the nice things about the Brompton is that you can partially unfold it (just raise the handlebars), and roll it along behind you like a cart. So if the train->office trip is too short to bother unfolding it, riding it, and folding it up again (though those are really quick, they take about 15 or 20 seconds), you could just raise the handlebars back up and walk it up to your office.
Watch the video I linked to, or skip to the last 5 minutes or so; that's a Brompton (slightly modified, the seat and seat tube usually stay attached), and you can see how quick and easy it is to unfold the bike and ride off.
Watch the video I linked to, or skip to the last 5 minutes or so; that's a Brompton (slightly modified, the seat and seat tube usually stay attached), and you can see how quick and easy it is to unfold the bike and ride off.