So one of my absolulte must stops was Paddington Station. We actually started here when we arrived on the Airport Express, but we had luggage and I didn't want to explore.
One of my close friends was expecting at the time and I knew she loved Paddington so I wanted to get her little girl a stuffed Paddington and book. I also wanted it to be authentic.
We stopped by the Paddington booth at the station and got to see the large bear himself.
So worth the stop. Also get some Millie's cookies if you're there because, yum.