As a professional for more than thirty years in the world of "touching-balls" (in possession of the proper european certificate) i will like to say that the photo appearing at the moment in which our dear narrator talks about the "National Portrait Gallery" is actually the entrance of the "National Gallery". Alright, it's the same building but, if following our dear narrator you enter the suposed "National Portrait Gallery" you won't find any portraits there, but still you will enjoy a very edificating cultural experience.
http://www.e-architect.co.uk/london/jpgs/london_building_aw050507_306.jpg