The author explains how they took these photos: http://blog.roberttimothy.com/2013/05/Deserted-empty-London-...
I was actually hoping he did something clever like take multiple shots and stitch them all together.
Ah well, I suppose this is more noble.
Take 3+ shots on a tripod then take the median value of each pixel. Anything that is moving (pedestrians, cars) will vanish.
Example: http://www.creativetechs.com/iq/photoshop_cs3s_automatic_peo...